Name one empire that was not tolerant of other religions or ethnic groups.

I would say great britain under the rule of king george?

It was the Roman Empire. As the Roman Republic, and later the Roman Empire, expanded, it came to include people from a variety of cultures, and religions. The worship of an ever increasing number of deities was tolerated and accepted. The government, and the Romans in general, tended to be tolerant towards most religions and cults. Some religions were banned for political reasons rather than dogmatic zeal, and other rites which involved human sacrifice were banned.