germany signs a treaty to have peace with the united states, Britain, france and the soviet union. The reason why germany retreated is because the Yalta Conference in February 1945 led to a further development of the terms of surrender, as it was agreed that administration of post-war.
the united states and soviet unions were not friends but since Germany was such a big enemy, they had to collab to defeat the Nazi soldiers, Therefore the answer is both, they were allies but they were never friends
the Manhattan project was a experiment about the first nuclear weapons of world war 2, this would play a huge role in war and the army would start bombing and spark a nuclear arms race, the manhattan project has a big impact of war til this day.
the united states wanted to end war as they wanted japan to surrender, they decided to bomb a city in japan called Hiroshima and they thought this would make japan surrender but it would end up in serious conflict, after this tragic event, japan would surrender in august 14 1945