All of the above. Many people left Eastern Europe for fear of religious persecution (this was around the time of WWII). People from Western Europe left because as America became a "land of opportunity" and capitalist venture, they saw many golden chances to make millions of dollars through the heavy industrialization of the northern states, like Michigan. Political freedoms were also a chance for people to have their voice heard and help others through legislation and politics. Finally, many people (even today) leave their countries to raise their kids in a 'safer' environment than their native countries (this is especially true for people immigrating from Central America, where gang violence is widely present) and in order for their kids to recieve a better education.