What is exclusivism in history??
I think this question can be handled in lots of different ways. History is filled with exclusions. In certain place and times, a gender is excluded. In other times and places, certain races are excluded. I think you get the picture. If we look at the history of America, we also can see the principle at work. At one point women could not vote. Voting was an exclusive act of men. At another time, slaves could not vote - again the principle of exclusion. During the civil rights movement, colored folks could not enroll in certain kinds of schools. Today, the debates have changed with our times, but the principle is still at work. What should be done with immigrant workers? Should they be excluded from health benefits, education, etc. I suspect that we will always be dealing with this principle.
In all my years teaching and reading history, I've never come across the term "exclusivism" except when it relates to religion.
In religion, the term refers to religions which believe that theirs is the only way to salvation or the only true religion. So, for example, ancient Roman religion was not exclusivist. It did not purport to be the only true religion. Instead, Romans believed that their gods were real, but that there were others.
By contrast, Christianity is an exclusivist religion because it believes that the only way to salvation is through Jesus and that other religions are simply wrong.
Is it possible that you are being asked this question in the context of religion? Let me know if you need more help.