To begin, a large number of the German immigrants to America came from the southern part of Germany, including Bavaria. Ireland wasn't the only country struck by potato blight, merely the one that had relied the most on the potato for the majority of the population, and massive numbers of Bavarians fled to America starting in the 1840s due to the same problem in the region. German populations were so high that a neighborhood in southern Manhattan was deemed "Kleindeutschland" until the turn of the 20th century, which was home to plenty of saloons selling lager.

The second part comes from the post-WW2 occupation of Germany. The country was divided between different zones controlled by different Allied countries, with America occupying the southern region that included Bavaria and Hesse. Americans returning home after their time on occupation returned with the idea of "Germany" being Bavaria, reinforced by the existing German families in America.