What manifest destiny actually was:

Imperialist phrase first used in 1845 to urge annexation of Texas; used thereafter to encourage American settlement of European colonial and Indian lands in the Great Plains and Far West; Created by John L. O'Sullivan; "overspread the continent allotted by Providence (God) for the free development of our yearly multiplying millions"

Explanation: Hope this helps :)

the manhattan project's indispensable man

on april 6, 1917, the u.s. joined its allies--britain, france, and russia--to fight in world war i. under the command of major general john j. pershing, more than 2 million u.s. soldiers fought on battlefields in france.