Because trains started and people started working for trains.
I think it's D a total war aimed at victory and reunification
I personally think it’s A
The land was free and perfect for farming, if settlers survived the journey to Oregon the land was all theirs. But not only did the US like it, Britain and Russia also liked it. So the US told people to move there ASAP so it would officially be claimed by America.
B and C
The Mayans were polytheistic (worshiped multiple deities) so A is incorrect.
They had their own form of hieroglyphics so B is correct.
The practice of astrology was one of the most important aspects of Mayan culture, and they supplemented their knowledge of the stars using math to figure out complex patterns so C is correct.
It was the Incas, NOT the Mayans who had runners, so D is incorrect.