I'm not quite sure about my answer, so I may be incorrect, but I think the answer would be C.
I'm just going with my gut instinct right now, so I may be incorrect.
It was important because it made you learn about how things change in History.
The term that said US expansion was God's will is the Manifest Destiny
The group that made up the majority of California's population in 1840 was Native Americans.
And finally, the first American settlers into the Mexican territory known as Texas in 1821 were brought by Stephen F. Austin.