The Mexican Cession is the huge tract of land that the US got from Mexico as a result of the Mexican American War. It is significant for two reasons.
First, it greatly enlarged and enriched the United States. The gold in California and the silver in Nevada were just two examples of the wealth of this area. Second, by obtaining the Mexican Cession, the US moved closer to the Civil War. The US had to decide whether the territories organized from the new land would be slave or free. This led to more conflict between the North and South and helped to bring about the Civil War.
The Mexican Cession was important to our history. After the war with Mexico ended, the Treaty of Guadalupe Hidalgo was signed. As a result, this treaty established our Mexican-United States border at Texas at the Rio Grande River. We also got California, Utah, and Nevada from Mexico. In addition, we got parts of Colorado, Utah, and New Mexico from Mexico. Getting all of these areas fulfilled our goal of Manifest Destiny, which was expanding our control over lands from the Atlantic Ocean to the Pacific Ocean. With the exception of a very small amount of land in southern Arizona and New Mexico, we now controlled the land in what makes up the lower 48 states.
Gaining this land also intensified the debate over the spread of slavery. Both the North and the South viewed these new lands as possible free states and slave states. There would be many discussions regarding these lands. In the Compromise of 1850, California would be allowed to join the United States as a free state. People would decide if there would be slavery in the Utah and New Mexico territories. Thus, while the Mexican Cession presented many opportunities, it also increased the tension over the spread of slavery.