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The Canaanites were idol worshippers.
Marvin Reynolds
The major call is based on one fact--stated in several parts of the Bible--they used children as sacrifices to the evil God they served. The incident lasted about 400 years til the Jews moved to take over Canaan Land and in this case they were ordered to obliterate all in the land. They did not do that resulting in the curse that followed them to this day.