According to the U.S. Census, more Americans self-identify as having German ancestry than any other group, and the peak of the migration seems to have been during the 1880s (1.5 million arrived just in that decade).
While I've learned much about the 'pull' factors during this time, which overlaps with the U.S. Gilded Age, I have struggled to understand what conditions 'pushed' German migrants to the United States. In some accounts of German history, this period is almost considered a Golden Age in that country. Germany had just unified, Bismarck was chancellor, and they had started to implement the world's first welfare state. This seems incongruous–if things were getting better in Germany, then why did so many leave?
Anti-Catholic Laws during the 1870s, and increasing militarization, including conscription, in conjunction with the rise of the modern German state played significant roles as push factors.
Rinehart Kondert's book on the Robert's Cove community in Louisiana offers some insights into the process of German migration to the U.S. during the late 19th century.