In the following, I will examine the complex geopolitical concerns, conflicts of ideologies, and strategic needs that shaped the two superpowers’ changing relationship from 1941 to 1945. Through an examination of crucial events such as the battle of Stalingrad, El Alamein, and Kursk, also the Tehran, Jalta, and Potsdam conferences, and the invasion of Normandy, this thesis aims to explain how the two countries became allies, how this alliance contributed to the defeat of the Axis powers. Additionally, the analysis also looks at how diplomatic discussions aided the US and the USSR establish a strategic alliance during World War II that ultimately led to the victory of the Allies, furthermore how the conflict between the US and the Soviet Union shaped post-war Europe.