How did the united states and the soviet union come to dominate europe after 1945?

Following WWII, the United States and the Soviet Union were the two most powerful nations in the world. WWI devastated Europe with many lives being lost as well as destruction to the landscape. WWII was even more destructive, both economically and politically exhausting great nations like France, UK, and Germany. Stalin, Roosevelt, and Churchill met at the Yalta Conference in 1945 to discuss the situation of postwar Europe. This later lead to a separation of Eastern Europe, (which went into Soviet hands) and Western Europe which America financially aided and sent supplies to to help rebuild.

I'm pretty sure that's called a volcano