Stronger rails allowed heavier goods to be shipped from one point to another. Larger trains allowed more load to be moved thus allowing an increase in what "people could be moved" If you have any other questions feel free to ask!
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.
The significance of Howard Carter's discovery of Tutankhamen's Tomb was that, it was the first royal tomb in modern times to be found intact with new information for archaeologists. The correct option among all the options that are given in the question is the first option or option "A". I hope the answer helps you.
