Due to the disagreements about the future of Europe between the USA and the USSR, the Yalta and Potsdam conferences were called to help the Allies decide what would happen to Europe, and in particular Germany, at the end of the Second World War. At the Yalta Conference in February 1945, Germany was not yet defeated, so, although there were tensions about Poland, the big three - Stalin, Roosevelt and Churchill - managed to agree to split Germany into four zones of occupation, and to allow free elections in Eastern European countries. A government of 'national unity' was to be set up in Poland, comprising both communists and non-communists. Russia was invited to join the United Nations, and Russia promised to join the war against Japan when Germany was defeated. When the Potsdam conference was held in July 1945, Germany had been defeated, Roosevelt had died and Churchill had lost the 1945 election - so there were open disagreements. There were arguments about the details of the boundaries between the four zones and the amount of reparations Russia wanted to take. Truman came away angry about the size of reparations and the fact that a communist government was being set up in Poland and that Stalin had arrested the non-communist leaders of the country. Truman dropped an atomic bomb so that Japan would surrender before Russian troops could go into Japan. America had the bomb in July 1945, but Truman did not tell Stalin about it. When he saw how he had been tricked, Stalin was furious and the Soviets began to suspect the Americans.
Stalin began gradually taking over East Europe with communism and was not sticking to the promises made at the Yalta and Potsdam conference. The Communists made sure that they controlled the army, set up a secret police force, and began to arrest their opponents. Non-Communists were gradually beaten, murdered, executed and terrified out of power. By 1949, all the governments of Eastern Europe, except Yugoslavia, were hard line Stalinist regimes. The West became very suspicious and concerned about the spreading of communism and feared that it was moving West. In 1946, in a speech made in the USA, Churchill declared that an Iron Curtain had come down across Europe, and that Soviet power was growing and had to be stopped. Stalin regarded the speech as a threat and called it a “declaration of war”.
By 1947, Greece was one of the few countries in Eastern Europe that hadn't turned communist. The Communist rebels in Greece were prevented from taking over by the British Army. America was becoming increasingly alarmed by the growth of Soviet power. So, when the British told Truman they could no longer afford to keep their soldiers in Greece, Truman stepped in to take over. In March 1947, he told the American Congress it was America's job to contain communism and stop it growing any stronger. This was called the Truman Doctrine. Stalin sees this as yet another declaration of war upon the Soviets.
In June 1947, The Marshall Plan was set up to help Europe recover, economically, from the war. Truman asked Congress for $17 billion to fund the European Recovery Programme nicknamed “The Marshall Plan” to get the economy of Europe going again. Congress at first hesitated, but agreed in March 1948 when Czechoslovakia turned Communist. The aid was given in the form of food, grants to buy equipment and improvements to transport systems. 70 per cent of the money was used to buy commodities from US suppliers: $3.5 billion was spent on raw materials; $3.2 billion on food, feed and fertiliser; $1.9 billion on machinery and vehicles; and $1.6 billion on fuel. Stalin denounced the Marshall Plan as imperialism and claimed that the USA was trying to spread its influence by controlling the industry trade of Europe. He saw the plan as an attempt to control Eastern Europe and so created the Molotov Plan, which prevented Eastern Europeans from accommodating the Marshall Plan.
At the Yalta Conference in 1945, the Allies had decided to split Germany into four zones of occupation. The capital, Berlin, was also split into four zones. The USSR took huge reparations from its zone in eastern Germany, but Britain, France and America tried to improve conditions in their zones; unlike Stalin, who wanted to wreck them. In June 1948, Britain, France and America united their zones into a new country, West Germany. On the 23rd June 1948, they introduced a new currency, which they said would help trade. Stalin was extremely hostile towards these actions taken by the US, he wanted a weak Germany, not a reunified one. Stalin believed the US was going back on the agreements made at the Yalta and Potsdam conferences and consequently, he responded by cutting of all rail and road links into West Berlin, formally known as 'the Berlin Blockade'. This was a high point of tension between the USSR and the West.
The West were furious at Stalin's actions and saw them as an attempt to control West Berlin, but they could not military force against the USSR as this would be seen as an act of war – which neither sides desired. So, instead, the West decided to supply West Berlin by air. Of course, Stalin was opposed to the airlift but he had no other choice but to back down because using military force, an act of war, was the only way to halt the airlift. On 12 May 1949 Stalin, humiliated, abandoned the blockade. Stalin's humilation did not improve the relations between the USSR and the West; when the US claimed victory, the Iron Curtain became permanent and Germany was divided into the Federal Republic of Germany (West Germany) and the Democratic Republic of Germany (East Germany) until 1990.
The world's two strongest powers rarely get along well because each is the main threat to the other; they will always compete for security and power. The vast differences between the USSR and the USA probably sparked off the tension between them. Their political systems, lifestyles and aims opposed the other's; this would have obviously prevented any stable agreements being reached between the two powers. I believe that the difference of opinion was the root of all the problems they faced and triggered the gradual worsening of relations. Certainly that was not the factor that contributed towards the deterioration of their alliance; each side made mistakes to agitate the other. When Truman decided to drop the atomic bomb upon Japan without informing Stalin, it created an increased suspicion between the two countries. The methods used by Stalin to spread communism, which involved non-communists being beaten, murdered, executed and terrified out of power, were brutal and, accordingly, the West became suspicious of the USSR, became concerned that communism was spreading and therefore took action. All actions taken by each side were opposed by the other, but the only definate way to stop the others actions was to use military force - especially concerning the Berlin blockade and the airlift. However, using military force would have been classed as an act of war, and war was the last thing the USSR or the USA wanted; perhaps the sole thing they had in common.