How had the USSR gained control over Eastern Europe by 1948?

i have my history igcse tomorrow and im kinda lost on this topic. how did the USSR manage to get Poland, Bulgaria, Hungary:
Romania, Czechoslovakia, and East Germany to join Communism by 1948? does anyone have any detailed notes on this?

Soon after World War II, the Soviet Union and its Western allies parted ways as mutual suspicions of the other's intentions and actions flourished. Eager to consolidate influence over a number of countries adjacent to the Soviet Union, Stalin pursued an aggressive policy of intervention in the domestic affairs of these states, provoking strong Western reaction. The United States worked to contain Soviet expansion in this period of international relations that came to be known as the Cold War.

Mindful of the numerous invasions of Russia and the Soviet Union from the West throughout history, Stalin sought to create a buffer zone of subservient East European countries, most of which the Red Army (known as the Soviet army after 1946) had occupied in the course of the war. Taking advantage of its military occupation of these countries, the Soviet Union actively assisted local communist parties in coming to power. By 1948 seven East European countries--Albania, Bulgaria, Czechoslovakia, Hungary, Poland, Romania, and Yugoslavia--had communist governments. The Soviet Union initially maintained control behind the "Iron Curtain" (a phrase coined by Churchill in a 1946 speech) through the use of troops, security police, and the Soviet diplomatic service. Inequitable trade agreements with the East European countries permitted the Soviet Union access to valued resources.