What reasons are given for the failure of these other professional leagues? do any of these leagues still exist?

What event brought the us into wwii? what conflicts happened after the us entered the war? i know the first part of this question, i need with the second part.

List three reasons why explorers began to explore new, and old areas. [[ps: doesn't explicitly say where. i think it's more in general.

How did europeans and africans displace native americans in north america’s predominant peoples?