I think the letter B is the answer
very well the war end and the armor in china use in war to keep then safe to not get hurt.
The majority’s vote sums up popular sovereignty
The correct answer should be Advances in Technology and Industrial revolution
Mexican-American war happened in the 40s so that's before 1860, while a war with Spain occurred in 1898 which is after the mentioned period. They did advance in technology exactly due to the industrial revolution. An agrarian revolution. An agricultural revolution didn't happen in the US because of the Long depression that slowed it all down.