Many of them came over because of the civil unrest they were facing in Germany. They brought over the hot dog (or frankfurter), the hamburger, sauerkraut, and sauerbraten.
Mostly because of religion. There was a lot of conflict between Catholics and Protestants. Now some of the food that they brought with them should be things like hamburgers because that is actually a German dish that Americans seem to enjoy so much; I would expect sausages too.
