Your family might have emigrated to the United States over a series of generations. My ancestor's brother Tonjes Jurgens Ehmen immgirated to the US in the 1860s, leaving behind one brother who stayed in Germany, married and raised a family.
That brother had 11 children of his own, all born in Germany. All but two of those children immigrated to the United States between roughly 1870 and 1890. One of the children who stayed in Germany and had several children of his own--including one who came to the United States in 1910.
For three generations, some members of the Ehmen family immigrated to America while others stayed behind in Germany. The immigrants originally settled where they had relatives, later moving on to other areas of the United States.
Were your ancestors part of a multi-generational chain of migration?