In post-WWII Europe, what was the Soviet Union doing that angered other countries?
In post-WWII Europe, many countries (including countries like the US that were not in Europe) were angry at the Soviet Union because the Soviets were trying to control as much territory as they possibly could. Some people within the countries they controlled were angry because they did not want to be communist and/or dominated by the USSR. Other countries were angry because they did not want communism to spread across Europe.
After WWII, the Soviet Union wanted to control as much of Europe (and particularly Eastern Europe) as they could. They wanted this for two reasons. First, they felt that it was important to spread communism across the globe because they believed communism was the right ideology for all people. Second, they wanted to have a large buffer zone of countries they controlled between them and any enemy powers. They did not want an enemy right on their borders the way Germany had been in WWII so they wanted “satellite nations” between them and the West so that it would be much harder for any country to invade them.
When the Soviets started to try to dominate other countries, many countries became angry. The people within some of the countries that got dominated were angry. Many did not want to be forced to live under communist rule. Millions of people like this ended up fleeing to Western Europe. Others (notably in Yugoslavia) liked communism but did not want the Soviet Union to control them. Finally, the countries of the West were angry. They did not like communism and did not want it to spread. They wanted the Soviets to allow people in every country to vote for their own form of government, but the USSR refused. The countries of the West feared that the Soviets were trying, in essence, to take over the world and that made them angry.