The answer is Germans.
German immigration in the United States was massive and contributed enormously to the country's settlement. The greatest flow of German immigration to America occurred between 1820 and the First World War, during which almost six million Germans emigrated to the United States. From 1840 to 1880, they were the largest immigrant group. The newcomers before 1850 were mostly peasants who sought the most productive land, where their intensive farming techniques would yield more fruits. They enriched the American gastronomy by introducing the "Pretzel", which is actually called bretzel or old brezzila, a word that derived in bretzel.