I like your question and bangdazap's reply, but I find that there is some confusion about the use of the term "racism". As a child in the 70s, I remember the famous PSA of a boy asking his grandpa what prejudice is. It seemed to me that racism was just one form of prejudice, and did not include prejudice based on religious beliefs or ethnic grudges among different people of the same race.

As far as prejudice among different white ethnic and religious groups, the answer is that it was very common. However, it is difficult to say precisely when prejudice based on religion and ethnicity becomes actual racism, based on biological/genetic differences.