Why did so many immigrants travel to the US (now compares to the 19-century)… And what did the British colonists do to the United States of America?

I check for plagiarism, please own answer and I give bonus ;)

How did manifest destiny encourage westward expansion? a.) people thought their lives would be easier out west. b.) adding additional territories to the west meant more land and opportunity for settlers. c.) mexico did not want to give up texas to the united states. d.) it was more expensive to live in the eastern part of the united states.