The leader of the USSR was Joseph Stalin. Hope this helps!
U.S entry into world war II caused the us army to take over the atomic research project being conducted at columbia university in the early 1940s.
Explanation:
Nuclear expedition and atomic research was one of the thrust area during world war II in United States. Two special type of nuclear weapons were generated by them in the year 1940. There was a competition in between Germany and U.S in discovering atomic bomb.
After world war I several concillation measures were taken but nonetheless worked out in its best. That's why world war II happened and U.S also enetred into the battle even after following the principle of neutrality. It compelled them to take atomic research project.
While WWI was fought in the trenches and used machine guns and poisonous gas, WWII was fought using modern artillery and machines utilizing more airplanes, ships, tanks, and submarines. Special operations methods were also developed during this war together with atomic missiles and secret communications.
