In my view, this is, for most of the fifty years in question, a relatively non-critical period of US history on which to focus our attention on immigration. Nevertheless, the important thing that did occur toward the end of those years was the potato famine in Ireland and the impact it had on America. In the late 1840s and the following years, the failure of the potato crop led to mass starvation among rural people in Ireland who were tenant farmers. There was massive immigration to the US, where they faced another kind of oppression similar to that of the British and Irish Protestants in their own country. American “nativists” were against allowing large numbers of “Papists” (Roman Catholics) into the country. However, the end result was an ethnic and religious diversity among the American population of European descent to a degree that hadn't existed before. Though discrimination against people of Irish descent continued for a long time, they eventually became part of the huge melting pot and were in some sense path-breakers for the larger waves of immigration from many other parts of Europe to the US in the decades after the Civil War.