 Built as a monument to the westward expansion of the United States, it is the centerpiece of the Gateway Arch National Park, which was known as the Jefferson National Expansion Memorial until 2018, and has become an internationally famous symbol of St. Louis and the Midwest.As the Midwest opened up to settlement via waterways and rail in the mid-1800s, Germans began to settle there in large numbers.The largest flow of German immigration to America occurred between 1820 and World War I, during which time nearly six million Germans immigrated to the United States.