Often, immigrants arrived with differences in appearance, culture, language and religion, which native populations saw as threatening to their beliefs, values and notions of what a society should be. But it is difficult to determine what constitutes an ethnic group. Ethnic identities, like those of a nation, are assumed to have objective and subjective characteristics. The objective characteristics include language, religion, race, territory and culture. But each of these is subject to interpretation by the subjective preferences of groups.
Religion also poses a number of problems.
Groups which subscribe to a common religion do not always belong to the same ethnic group, and vice versa. Muslim Kurds are unhappy with the way they have been treated by Muslim Iran, Iraq, Syria and Turkey. Yoruba Muslims in Nigeria emphasize their Yoruba ethnic identity rather than their Islamic identity in their political relations with the predominantly Islamic Hausa-Fulani. Not every ethnic group possesses a distinct territory. Indeed, before the state of Israel was created in 1948, the Jews were without any territory they could claim as their own, even though many of them were conscious of their ethnicity.