Germany was divided by the allies after WWII, with Berlin in the USSR sector. As the US, UK and French zones had economic success, people left the USSR zone to move west. This caused Stalin to enforce a blockade of all goods between the western zones and Berlin, hoping it would run out of supplies quickly.
Hungary was poor, had a brutal police and strict censorship. They hated Soviet control and rebelled, but were swiftly put down by the USSR sending 6,000 tanks.
Khrushchev ordered a massive wall to be built dividing the city, to stop people escaping the USSR to the capitalist West. Anyone trying to escape would be shot.
Dubcek became leader of Czechoslovakia, promising more freedom and economic reforms. Brezhnev ordered 400,000 Soviet troops to invade, ending the reforms.
Korea was split between communists in the North and capitalists in the South. North Korea, supported by China and the USSR, invaded the South. The UN, led by the US, fought to defend the South.
The US supported South Vietnam to stop the spread of communism from North Vietnam. They used tactics like napalm and Agent Orange, but struggled to defeat the Vietcong guerrilla tactics. The war was unpopular in the US and they eventually withdrew in 1973.
The USSR invaded Afghanistan in 1979 to exploit its resources and stop Muslim unrest. The US supplied weapons and money to the Afghan Mujahideen fighters, who used guerrilla tactics. The USSR eventually realised they couldn't win and withdrew in 1989.
Gorbachev's policies of Glasnost (openness) and Perestroika (restructuring) led to the collapse of communist regimes in Eastern Europe. The Berlin Wall was opened in 1989 and Germany reunified in 1990. The USSR itself dissolved in 1991.
Tensions emerged with groups like Al-Qaeda and Saddam Hussein's Iraq. The US launched a 'War on Terror' in response to the 9/11 attacks, invading Afghanistan and Iraq.
The 9/11 attacks involved four planned attacks - two planes flew into the Twin Towers in New York, one into the Pentagon, and one crashed in a field after passengers fought back against the hijackers.
The US response to 9/11 was the 'War on Terror', fighting terrorists like Al-Qaeda and removing governments that supported terrorism, as well as improving security for US citizens.