Why were the steel plow in the mechanical reaper important inventions?

How did the nazis lead germany to war in europe and, with their collaborators, kill millions—including systematically murdering six million jewish people?

What happens after a star goes supernova? just wondering! [tex]supernova [/tex] answer asap i really wanna know!

What was the name of the theory that said that if one country in a region fell to communism, others would surely follow? 1) domino theory 2) arms race 3) brinkmanship 4) containment theory