What is the effect of low precipitation in the Southwest region?

Intrusion is the best answer and the newest form.

Ibelieve the answer would be a large-scale natural disaster 

The first immigrants to settle in what is now the united states were the ancient ancestors of modern native americans. the precise routes of those first north american immigrants are disputed, but there is no uncertainty about the fact that every human being on the continent is either a recent immigrant or a descendant of earlier immigrants. since the first immigrants came here from asia more than thirteen thousand years ago, there have been four large and easily recognizable modern waves of immigrants into the united states.

It's false or true. it's gotta be one of them