Answer:
The Mexican army attacked them. The main cause of the war was the westward expansion of the United States. All through the 19th century Americans believed it was their right to expand westward. At the time they believed they could conquer the people already living on the land and take it for the United States.
Explanation:
The main factor that influenced African Americans to migrate from the South to Northern cities was that they were looking for better economic opportunities.
The Great Migration, also known as the Great Northward Migration in the 20th century, happened because most black people were badly treated by many people that still expected African Americans to be slaves, and their economic conditions were quite poor.
As a result, African Americans decided to migrate to the Northern cities, where they would get many job opportunities as well as going to have a better lifestyle by not being discriminated.
Christopher Columbus is the answer most likely to be correct but, there is an argument for Leaf Erikson
The KKK was a democratic rasical group whom did not like the African Americans. They did not want the blacks to have any rights because they hated them a lot. I mean it's kinda obvious