White Ethnics

During discussion in class yesterday I realized that we group the smaller branches of whites into one the same way we have non-whites. Just like there are many different paths which lead a person to be "black", there are different paths followed that are all determined as "white". It seems like people take less offense to the grouping of white people. Why? I have spent time becoming in touch with my roots and where I come from and I should be able to hold onto that history like any other person, right? I understand that people see color, but why is it more acceptable to group in some cultures than it is another? And if we aren't going to acknowledge where we came from then why is it so difficult to agree that we're all American I wonder.