History how did the u. s. initially react to war breaking out in europe in 1939? question 2 options: the united states began mobilizing troops in anticipation of entering the war later. congress encouraged the league of nations to provide assistance. the united states offered europeans many more opportunities to immigrate. congress stressed isolationism and passed five neutrality laws. question 10 unsaved what was harry truman's justification for the use of atomic bombs to end world war ii? the us wanted japan to suffer for attacking pearl harbor. the us wanted to brag to the world about our new power. the us wanted to end the war with fewer us and japanese casualties. we wanted to destroy japan's atomic weapon facilities.