The stream of immigration of Germanic peoples to this country can be divided roughly into three periods: the late seventeenth-century migration centering near Philadelphia; the influx of Swiss Mennonites, as well as Lutheran and Calvinist Palatines, into the area known today as the Pennsylvania Dutch country, which began about 1710 and lasted in varying strength until just before the American Revolution; and the third wave in the nineteenth century, resulting from political upheavals in Germany, which chiefly washed the mid-west.