Conflict between racial and ethnic groups has been a problem throughout history, and is still a major problem today. Three underlying reasons for conflict between racial and ethnic groups are religious differences, racist upbringings of children, and a history of conflicts between racial and ethnic groups.
Religious differences have brought about conflict from as far back as the start of recorded history. Religious differences brought conflict during the times of Jesus Christ, and are well evidenced in the Bible. During the Crusades, battles were fought as a result of religious differences, in an effort to spread Christianity throughout the Europe and the rest of the world. Even today wars are still fought over religion, and this is particularly the case in the Middle East. Palestinians and Israelis are constantly feuding for control of "holy lands," and their religious differences are the primary cause of conflict. Religious differences are a major cause of conflict between racial and ethnic groups.
Racist upbringings of children are also a major cause of conflict between racial and ethnic groups. By raising children to be racist towards a particular race or ethnicity, racist groups further the prosperity of their groups by "passing the torch" so to speak, to the next generation, the youths of the racist movement, thus ensuring the future of the racist movement. The confederate states were notorious for furthering racism towards African-Americans during the 19th century, as a result of how their children were raised.
The history that racial and ethnic groups already have between one another also is a primary reason for conflict between racial and ethnic groups. While racism in America seems to be less of an issue now, than during the early years of the country, the simple fact that racism was present before is a motivating factor for conflict between whites and African-Americans today.