In May 1945, three months after the Yalta Conference, Allied troops reached Berlin. Hitler committed suicide. Germany surrendered. The war in Europe was won.
The Americans had developed and successfully tested a new weapon of tremendous and terrible power, and it would affect the future of relations between the superpowers.
Although they agreed about dividing Germany into four zones, Stalin wanted to cripple Germany completely to protect the USSR against future threats. Truman did not want to repeat the mistake of the Treaty of Versailles.
Stalin demanded $10 billion compensation from Germany. Truman resisted this demand, determined not to repeat the mistakes made at the end of the First World War and create a bitter, unstable Germany.
They disagreed over Soviet policy in Eastern Europe
At Yalta, Stalin had won agreement from the Allies that he could set up pro-Soviet governments in Eastern Europe. Truman saw this as evidence that Stalin wanted to build up a Soviet empire in Europe and adopted a 'get tough' attitude towards Stalin.