Known as the Yalta conference, Roosevelt, Churchill and Stalin met to decide how to divide up the broken nation of Germany, to prevent any more troubles or uprisings.
The bombs used at Hiroshima and Nagasaki shocked the world and brought to them the realization that nuclear weapons were basically a terrible idea, granting intense death powers to whoever owned them.
In order to prevent powers from rising to threaten peace, the Allies needed to unite and create a more effective League of Nations. Thus, the UN was formed.
The containment policy, proposed by George Kennan, detailed that in order to prevent the spread of communism to democratic nations, the democratic properties would overpower and surround communist properties, thus 'containing' them.
This was the beginning of a period in which America financially aided countries that, due to the war, needed the financial support, such as Greece and Turkey, initially. They then offered this support to the other United Nations.
Due to increasing fear of Communism and its spread over democracy, America cracked down on its content, calling out those who were speculated (and sometimes actually were) communist, or in league with communists, and forcing its citizens to root them out.
In order to weaken the West, the Soviet Union blockaded Berlin off from the UN. However, US and Britain planes were able to fly over and give the struggling Berliners needed supplies.
This was the first weapon exploded by the Soviet Union, putting stress on the other nations given that Russia should have not developed the technology, research, or knowledge this quickly...
Because of both the growing threat of the Soviet Union and nationalist militarism that might threaten the peace that the UN protected, as well as to bolster and enhance political integration, the US and basically the UN came together to form NATO.
Split in half by two opposing regimes, things are relatively stable in Korea until the Northern half unexpectedly launches an invasion on its Southern counterpart, starting a struggle to push the other side off of the map.
One of the most famous case of American anti-Communist investigations, two people rumored to be in league with the Soviet Union, Ethel and Julius Rosenberg, were executed, despite a popular demand to not do so.
After an attempt to get rid of communist Korea and China with nuclear weapons (and as a result, instigating nuclear war), General MacArthur was laid off for his behavior and demands by Truman. This caused a little bit of an uproar courtesy of MacArthur's fans, but after glancing at the big picture the general consensus was that this was for the best.
This pact pulled all of the existing Communist parties and nations together as a defensive alliance to rival the likes of NATO, thus making their presence stronger.
An unsuccessful invasion started by unhappy Cubans funded by the US, this served as another failure for the containment of communism, but was also an embarrassment for the US foreign policy.
Tensions ride extremely high as the US obtains pictures of multiple, first-strike nuclear weapons aimed in their direction parked in Soviet-controlled Cuba. The US installed a blockade around Cuba in order to prevent the bombs' arming, and after a declaration that basically stated that if they were attacked, they would attack back, the US was able to dismantle at least some nuclear ballistic weapons at the consent of the Soviet Union.
After many years, the previous Soviet leader Mikhail Gorbechev stepped down from his position due to the Soviet Union basically dissolving, as all but one of the original nations had abandoned the Union.