One example would be economic opportunities. The possibility of a better job would pull someone to a new country. Hope that helps!
After World War I, the United States had adopted a policy of isolationism, where they would not participate in global warfare or officially join the League of Nations. Roosevelt delivered the Four Freedoms speech 11 months before the United States declared war on Japan. The Four Freedoms speech was a break from the previous period of anti-interventionism, and described how the United States would be willing and able to assist its allies already at war.
They fought for better wages reasonable hours and safer working conditions.
John Locke helped develop the idea of a social contract between citizens and the "government", through was he believed was a "social contract" that allowed people to give up certain freedoms for the benefit of society.