Because there were messages intercepted from Germany to Mexico, telling Mexico to join the war and attack the United States. I hope this helps :)
The Louisiana Purchase was actually when the USA bought present-day Louisiana from France; it added French influences into our country, as well as more land.
C
It was to raise environmental health concerns that directly impacted American Indian reservations.
The word that would best describe the effect on each of these four groups would be regression.
