The Manhattan Project was a program set up in 1942 found by United States, United Kingdom and Canada. The project was mainly aimed to produce a powerful weapon that would change the revolution of warfare. The essay is focused on the question: "To what extent did the Manhattan Project contribute to the Cold War tensions among USA and the Soviet Union between 1942-1949?" The Manhattan Project started the atomic arms race between the two superpowers at the period of 1942-46. During the period of 1942-49 USA and USSR already had hostilities between them and many historians' asses the start of the Cold War earlier than the development of atomic weapon.
In order to assess the extent of contribution of the Manhattan Project to the hostilities between USA and USSR, the consequences and the events within the scope of 1942-1949 are analyzed. The judgment would be contributed by factors which arose from the Manhattan Project. These include the peace conferences held during that period of time such as the Tehran, Potsdam and the Yalta Conference. Hiroshima bombing and was USA's response to the Pearl Harbor attack from Japanese naval forces. All of these events did play a big role in the development of Manhattan Project and the hostilities between USA and Soviet Union, but many other factors and events had their role in increasing these hostilities.
The research and the study supported that the Manhattan Project in a large extent played a big role in development of the Manhattan Project as well as its start. However many other factors also had their own role in these developments. Hence the conclusion reached is that Manhattan Project to a large extent contributed to the further tensions of the Manhattan Project, with many other events which had comparably smaller contribution to the tensions.
Overview of the Manhattan Project:
The idea of the atomic weaponry started in 1919 from the discovery which was made by a famous New Zealander Ernest Rutherford. This scientist was trying to achieve what was impossible to be achieved, in a laboratory in Cambridge University in England. He succeeded in developing the first transmutation of an element when he changed several atoms of nitrogen into oxygen.  After this event in 1932 a college of Rutherford and he were able to identify the particles that were present in the atom. In the same year a more important event in atomic physics happened where  Englishman J. D.Cockroft and Irishman E.T.S Walton, were the first people who split the atom when they bombarded lithium with protons. These events show the progression and the hardness of this atomic theory behind all these events. And these events prove that the Manhattan Project was a huge scientific boost for the United States. However it was only in 1939 when US presidency who was Roosevelt at that time took part in the funding and planning of this project that was aimed for the US to end the WWII. When Roosevelt firstly received a letter from Albert Einstein, the German physicist with the claim for funding of a project which was based on the research upon uranium. After receiving Albert Einstein's letter, Roosevelt started planning the committee which would deal with creating a secret project under the name of Manhattan Project. The British supported US by providing with scientists to the different districts of Manhattan Project. After having a successful development of uranium extraction and research in 1942 it was the official beginning of the Manhattan Project aimed mainly at the creation of the Atomic Bomb itself.
The Aftermath of the Manhattan Project:
The Manhattan Project's main contribution to the tensions between USSR and USA were in terms of Nuclear Arms race. As USA had advanced the Atomic Bomb a misbalance was created between the two superpowers, providing USA with confidence in enforcing their policies consisting of realpolitik purposes. At the same time in August 1949 USSR is able to create its own atomic bomb which creates fear in USA. Manhattan Project increased the tensions between USA and USSR when the Atomic Bomb was used in Hiroshima and Nagasaki. The reason behind the bombing is complex, but this decision can be explained by the Japanese attack on Pearl Harbor. However Pearl Harbor wasn't the only reason, as USA's bombing in Japan exposed Truman's new approach to USSR. During  Yalta Conference (1945) both USA and UK wanted USSR to participate in war with Japan, however the news about the successful tests in  Trinity Zone changed USA's decision. Same change in attitude happened to Stalin, and the creation of Soviet bomb was boosted by his command after the Potsdam conversation between Truman and Stalin. Stalin becomes more active in the Eastern Europe by having more sphere of influence, and this change in attitude created different issues in Eastern Europe. Such as the Berlin Blockade and USA's approach to these actions was the establishment of Truman Doctrine and the Marshal plan, which then was followed by the creation of the organization called  NATO.
The Manhattan Project created a gap between the military powers and sphere of influence in the world which led to the creation of Soviet Atomic bomb. This led to the Nuclear Arm's Race, later on the tensions were exposed in the Eastern Europe where realpolitik's was the main reason for the two superpowers conflicts over the Eastern Europe. Hence the Manhattan Project to a large extent had a contribution to the Cold War tensions between the period of 1942-49 by building up different issues around the two superpowers and making the war a "Cold" war.
News of the Atomic Bomb in Potsdam Conference.
The Potsdam conference incidence is a reason of the message which Truman got about the successful achievements of their Atomic Bomb. It was during the peace conference in Potsdam held in July 24th in 1945, where Truman had received a message about the first achievements of the Atomic Bomb and the successful testing results. After having something more powerful than the USSR had Truman's attitude changed towards the Soviets and no more thoughts about establishing peaceful relations with the USSR were still in his mind. During that conference a very important incident happened where Truman had a conversation with Stalin about USA's achievements in creating a new weapon. Around this incident many different historians have different perspective around it, however one of the important documents which gives evidence about the intentions of this conversation is from accounts of different observers. The version from  British Prime minister's account suggests that Stalin's lack of knowledge about technology and science was the reason for his behavior as he didn't ask questions from Truman he kind of ignored and nodded to him. However at the same time from Georgii Zhukov's version, Truman wanted to show himself to Stalin with their new weapon. However Zhukov states that just after the conversation Stalin messaged Molotov to speed up the process of the research. So after the meeting in Potsdam where Truman informed Stalin about the bomb, Stalin summoned Molotov and Soviet foreign minister Andrei Gronyko, where he announced: "The USA has a new weapon..", and that the development of Soviet bomb should be accelerated. However  Zhukov states that Stalin already knew about the Manhattan Project and its beginning from Soviet spies in the area of USA. And Zhukov's idea is that USA's main aim for the creation of the Atomic Bomb was simply to succeed in its imperialistic goals and they started with Japan with the Bombing of Hiroshima and Nagasaki. However these accounts show the different prospective of the people who heard the conversation, the limitation is that Zhukov could have just mentioned about Stalin knowing about it only in order to keep Soviet Union's position as a super power as well and Stalin as the smart leader. Hence the beginning of the effects of the atomic bomb on the course of Manhattan Project starts from the Potsdam conference, as it is where the unbalance or the gap between the two superpowers is created. And also still in 1945 but in August the Americans actually use their atomic bomb on Japan.
During the conference in Yalta the intentions and views which Truman had was different from what he had during the Potsdam conference. The reason behind these changes is due to the Atomic Bomb development in USA. Therefore the Atomic Bomb contributed to the tensions of the Manhattan Project during the period of 1945. So what happened was in  Yalta Conference the War with Japan was getting very hard for USA and Britain to handle, and they agreed that USSR would attack Japan in order to end the War with Japan. However the incident which happened in Hiroshima where the American bomber drops the atomic bomb, shows the contrast between the Yalta Conference agreement and the actions which USA did afterwards. This is an evidence of how the atomic weapon became a big part of the Cold War tensions. As a result of the USA's actions USSR's troops were still in the boarder of Manchuria waiting for the attack order, and this is where Stalin orders them to conquer Manchuria. Stalin in 1946 announced a gathering in Moscow where he gave his important speech called the Bolshoi Speech. The Bolshoi Speech Stalin Mentioned:  "'The development of world capitalism proceeds not in the path of smooth and even progress but through crisis and the catastrophes of war...". The speech showed Stalin's attitude on the Hiroshima bombing. The Manhattan project in which led to the success of making US atomic Bomb influenced Truman's attitude in Potsdam and the defoliation of US and USSRs relations.
The Decision to use the Atomic Weapon:
The biggest event which happened on  August 6 1945, was when USA dropped its atomic bomb on a city called Hiroshima in Japan. According to the agreement in Yalta the Japanese invasion was to be held by cooperation between America USSR and Britain. However the use of Nuclear weapon allowed USA and Britain to establish the Japanese surrender. The decision made by Truman to drop the atomic bomb is still a controversy topic to investigate. However the decision was influenced due to the Cold War tensions. The revisionist historians of the Cold War state that the decision to use the Atomic weapon made the USA to be blamed for the tensions of the Cold War. However the Revisionists asses that the Atomic Weapon gave end to the Japanese War and in a long term prevented the war to shift from  Cold to  Hot war. And finally the  John Lewis Gaddis, a post-revisionist historian states: that USA's main aim was to end the war with Japan, however Truman and his advisers expected their new weapon to bring a more conciliatory attitude on the part of the USSR. However the aftermath of the Hiroshima bombing were seen from the Soviet response to it. "Hiroshima has shaken the whole world", Stalin told his scientists in approving a Soviet program to catch up. "The balance has been destroyedâ€¦ That cannot be resolved."  The Atomic Bomb prevented USSR to have it's role in the Japanese war, Stalin saw that the bomb was also used in order to provide USA with a chance to extract postwar concerns from the Soviet Union. As a result of this Stalin pushed his policies into much harsher type and denounced the reason for the Hiroshima bombing, and he decided that the only way was to demonstrate USSR cannot be frightened. "It is obvious," he told his advisers in late 1945, "thatâ€¦we cannot achieve anything serious if we begin to intimidation or betray uncertainty". 
The use of the Atomic Bomb in Hiroshima therefore angered USSR and Stalin took the strategy to not show his knowledge about the bomb. This allowed him to work on his own bomb and therefore the Atomic Era moved into an Atomic Arms Race which in a long term took up to the Cuban Missile Crisis in 1962. Where the two superpowers were very close in starting a Hot War between them.
If it wasn't the Manhattan Project and the development of Science and technology the Atomic Bomb wouldn't have been created. Therefore the Cold War wouldn't have been as important and critical as it was. The reason is because the two Superpowers used the threat of it's use on each other in order to push forward their policies throughout the world. Also the Bombing in Hiroshima led to the increase in development of tensions between USA and USSR as the agreement was broken by USA about Japan. Hiroshima bombing by USA left the Soviet soldiers on the border of Manchuria and the role and power of USSR in the world went down, compared to USA.
Soviet Development of Nuclear Weaponry:
Following the Manhattan Project the Soviet development of Nuclear Weaponry increased its speed. Joseph Stalin realized that the USA development and success in Atomic Bombs would increase the US influence in the World by Nuclear monopoly. A historian called Hugh Higgins in "The Cold War" (1974) claimed that Stalin called Truman's bluff:  "He acted on the assumption that the atomic bomb was a 'paper dragon'â€¦He put priority in the making of a Russian bomb and at the same time refused to be feared by the American bombs'. Soviet Atomic weapon development started from 1943 and was successful to create it's own bomb only 4 years after the Hiroshima Bombing. However until the success in the Trinity tests Soviet Union didn't have the knowledge about nuclear warfare and its effects. And only after the US success Soviet Union started an intense program of developing their own bomb. During the years of 1942-49 the economic condition of USSR wasn't strong enough for these kind of investments however Stalin saw the development of the Atomic Bomb as his first priority. During the late 1930's Soviet Union had great scientist who were working on the investigation of splitting the atom and using nuclear reactions to create bombs.
Therefore the Manhattan project leading to the Hiroshima Bombing demonstrated Stalin how the Atomic energy could be used in warfare which motivated the scientist to boost the development of Soviet Nuclear bomb. However not only the Soviet development of their atomic weaponry, but Truman's foreign policy changed drastically after the news of the US success in New Mexico. Hence leading to further tensions in the relationship between USA and USSR.
The US foreign Policy and the Eastern Europe, between 1945-49:
After the successful tests in Trinity zone, US foreign policy from 1945-49 seemed to be harsher on the Soviet Union and there was an increase in US sphere of influence. The US isolationism which broke from the Pearl Harbor Attack transformed into a more influential nation in resolving international issues. Following the same year of 1945, USA used the bomb and Japan surrenders. From 1945-47 the  Marshal Mission was in action which was aimed to contain the communist power in China. Therefore the creation of atomic bomb influenced Truman's decisions in terms of US foreign policy which in a long term caused more tensions between USA and USSR. The events during the period of 1945-49 were: the establishment of United Nations, George Kennan's Long Telegram, Marshal Plan and the Truman Doctrine. Finally in 1949 the NATO is formed by the US which is the first strongest organization aimed at containing Soviet influence in the World. The areas which are connected with the Manhattan project are the: Berlin Blockade, George Kennan's Long Telegram and Churchill's iron curtain speech.
Following the Bolshoi speech another important aspect of the Cold War which was also a consequence of the Atomic Bomb and the USA's confidence is George Kennan's Long telegram which was a long telegram written in February 22 in 1946. The telegram enforced the policy of USA's containment, and As Kennan had huge experience in Soviet history from the purges up to the Cold War era, he was able to study Stalin's actions and his long term aims, in form of Soviet foreign policy. By serving as a deputy head of United States envoy in Moscow, from 1944 until 1946, he was able to write in the end a Long Telegram. It was interpreted as USA's reply to Stalin's Bolshoi speech. Kennan emphasized upon the plans of USSR's foreign policies in terms of expansion into the Eastern Europe with the spread of communism and therefore increasing Soviet sphere of influence in the world. Another great aspect of the  Telegram was about the instability of the Soviet History starting from the Tsar till the days of the Cold War, and associating the USSR as a weak country where dictators are able to rise easily and control the people. However another big factor which can also be interpreted as the main reason for the Cold War is the Ideological difference between USA and USSR. The reason is because USA was against communism ideology and USSR was communist. Even the US foreign policies include policies which are directed against the spread of communism in the world. Therefore from a different perspective it was the communist ideology which resulted in the tensions and the creation of Cold War. The evidence for that is from the George Kennan's Long Telegram and the creation of NATO in 1949. However the Telegram was a result of the Manhattan project as well because it was a reply for the Bolshoi speech by Stalin. And the reason for the Bolshoi speech is the Hiroshima Bombing and the Manhattan project.
Another important US policy which influenced the tensions of the Cold War were the Marshall Plan and the Truman Doctrine. These two policies were started in 1947 aimed at Hungary, Turkey, Czechoslovakia and  East Germany. However the reason behind the implementation of these policies were the seizure of power of communists throughout the world. The Soviet Union started increasing its sphere of influence even more after the 1945 Hiroshima bombing. As USA tried to intimidate USSR with this action Stalin however tried to act smarter, with a good strategy  . Stalin's main action which showed the US that it wasn't intimidated was the Berlin Blockade in 1948. The reason behind the Soviet increase of its sphere of influence is hidden under the Soviet Economic condition. As the US was able to create their own weapon, USSR was its own way to make its own. However USSRs economy wasn't strong enough to be able to accommodate the construction of Atomic Bomb. Also the  Uranium supplies were limited for USSR compared to US supplies and this gap was filled only by the Soviet supply form  East Germany.
The creation of North Atlantic Treaty Organization:
The Final and Vital event on 1949 which was the signing of the  NATO agreement was as a long term result of the Manhattan Project. The reason is that the Manhattan Project gave USA a chance to bomb Hiroshima. Which then alarmed the USSR, and influenced USSR's foreign policy as well as USA's foreign policy. And due to the tensions in East Germany, USA implemented the NATO organization. The agreement was that if any country attacked a country in Europe or North America it would be considered as an attack against all of the members of NATO. A collective self-defense would then join in the conflict and help to resolve it. This meant that USSR's sphere of influence in forcing countries to become communist will be limited and controlled. This therefore in a long term increased tensions between USA and USSR as USSR made the Warsaw Pact. It consisted of USSR's allies who agreed to similar agreements as the NATO members. These two organizations later on, during the Cold War competed with each other on terms of territorial positions and military power.
However the NATO can be seen as a resolving and peace move from the US side. As this allowed more countries to be together so no any conflict would arise. The evidence behind this is that USA and USSR didn't have a Hot War between each other during that period. NATO was able to resolve many conflicts which arose during time period (1949-91). But NATO only in a long term resolved the tensions between USA and USSR.
Overall the investigation was supposed to assess what the major factor was in the tensions between USA and USSR between 1942-49. The conclusion is that the Manhattan Project to a large extent played a big role in increasing tensions between USA and USSR between 1942-49 leading to a term called: Cold War. The Manhattan Project moved the Hot War into a Cold War as both countries tried to prevent a nuclear war between them. The aftermath of the Manhattan Project was the success in the Trinity test, where the first US nuclear fission bomb was tested. Following this event the Potsdam Conference followed where Truman and Stalin met and Truman told Stalin about their achievements. Also by hearing the news about the test results in New Mexico, Truman changed his Cold War strategy against Soviet Union. USSR on the other hand boosts its development of nuclear weapons and catches up with USA in 4 years. Leading to a nuclear arms race. The resources in the East Germany helped USSR to create its own weapon and also this led to the Berlin Blockade where Germany was divided into 4 zones. In the end where USA saw the expansion of USSR with realpolitik aims, NATO was formed by USA in order to fight against spread of communism. NATO was the final event due to the other events caused by the atomic bomb which contributed to the Cold War tensions between USA and USSR. However the Manhattan Project in the long term prevented the Cold War to turn into a Cold War.
Overall The Manhattan Project contributed to the creation of series of events, which all had their influence on the US and Soviet relationship. Hence to a large extent, the Manhattan project played a big role compared to other issues in increasing tensions between USA and USSR between 1942-49.
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Appendix: 1 
An extract from Stalin's Bolshoi Speech:
Joseph VissarionovichÂ StalinÂ has the floor.
Â Â (Comrade Stalin's appearance in the rostrum was greeted by the voters with loud cheers lasting several minutes. The entire audience in the Bolshoi Theatre rose to its feet to greet Comrade Stalin. There were continuous cries of "Cheers for great Stalin!" "Long live great Stalin,Â Hurrah!" "Cheers for our beloved Stalin!"Â )
Â Â ComradeÂ Stalin:
Â Â Comrades!
Â Â Eight years have passed since the last elections to the Supreme Soviet. This has been a period replete with events of a decisive nature. The first four years were years of intense labor on the part of Soviet people in carrying out the Third Five-Year Plan. The second four years covered the events of the war against the German and Japanese aggressors -- the events of the Second World War. Undoubtedly, the war was the main event during the past period.
Â Â It would be wrong to think that the Second World War broke out accidentally, or as a result of blunders committed by certain statesmen, although blunders were certainly committed. As a matter of fact, the war broke out as the inevitable result of the development of world economic and political forces on the basis of present-day monopolistic capitalism. Marxists have more than once stated that the capitalist system of world economy contains the elements of a general crisis and military conflicts, that, in view of that, the development of world capitalism in our times does not proceed smoothly and evenly, but through crises and catastrophic wars. The point is that the uneven development of capitalist countries usually leads, in the course of time, to a sharp disturbance of the equilibrium within the world system of capitalism, and that group of capitalist countries regards itself as being less securely provides with raw materials and markets usually attempts to change the situation and to redistribute "spheres of influence" in its own favor -- by employing armed force. As a result of this, the capitalist world is split into two hostile camps, and war breaks out between them.Â Perhaps catastrophic wars could be avoided if it were possible periodically to redistribute raw materials and markets among the respective countries in conformity with their economic weight by means of concerted and peaceful decisions. But this is impossible under the present capitalist conditions of world economic development.
Â Â Thus, as a result of the first crisis of the capitalist system of world economy, the First World War broke out; and as a result of the second crisis, the Second World War broke out.
Â Â This does not mean, of course, that the Second World War was a copy of the first. On the contrary, the Second world differed substantially in character from the first. It must be borne in mind that before attacking the Allied countries the major fascist states -- Germany, Japan and Italy -- destroyed the last remnants of bourgeois-democratic liberties at home and established there a cruel terroristic regime, trampled upon the principle of the sovereignty and free development of small countries, proclaimed as their own the policy of seizing foreign territory, and shouted from the housetops that they were aiming at world domination and the spreading of the fascist regime all over the world; and by seizing Czechoslovakia and the central regions of China, the Axis Powers showed that they were ready to carry out their threat to enslave all the freedom-loving peoples. In new of this, the Second World War against the Axis Powers, unlike the First World War, assumed from the very outset the character of an anti-fascist war, a war of liberation, one of the tasks of which was to restore democratic liberties. The entry of the Soviet Union into the war against the Axis Powers could only augment -- and really did augment -- the anti-fascist and liberating character of the Second World War. It was on this basis that the anti-fascist coalition of the Soviet Union, the United States of America, Great Britain and other freedom-loving countries came into being and later played the decisive role in defeating the armed forces of the Axis Powers. That is how it stands with the question of the origin and character of the Second World War. Everybody, perhaps, now admits that the war was not nor could have been an accident in the lives of the peoples that it actually became a war of the peoples for their existence, and that for that very reason could not have been a swift or lightning war. As far as our country is concerned, for her this war was the fiercest and most arduous ever fought in the history of our Motherland. But the war was not only a curse. It was also a great school which examined and tested all the forces of the people. The war laid bare all facts and events in the rear and at the front, it ruthlessly tore down all the veils and coverings that concealed the actual features of slates, governments and parties, and brought them onto the stage without masks and without make-up, with all their defects and merits. The war was something in the nature of an examination of our Soviet system, of our State, of our Government and of our Communist Party, and it summed up their work and said, as it were: Here they are, your people and organizations, their life and work scrutinize them carefully and treat them according to their deserts.
An extract from George Kennan's Telegram  :
Telegram, George Kennan to James Byrnes ["Long Telegram"]