part 1:, Texas was admitted to the United States a slave state. The annexation of Texas contributed to the coming of the Mexican-American War (1846-1848). The conflict started, in part, over a disagreement about which river was Mexico's true northern border: the Nueces or the Rio Grande.
This site might help:
https://www.khanacademy.org
part 2: The discovery of gold in 1848 by James Marshall sparked a massive wave of westward migration. The largest influx occurred in 1849, and those prospectors who sought their fortunes became known collectively as forty-niners, in reference to the year they arrived.