God ordered the destruction of the cannanites because if the corrupting influence they will have if their false religious system was allowed to thrive. Unfortunately, Israel disobeyed God and didn't not fully destroy the cannanites, this singular act of disobedience made God angry with the Israelites and he made all of the statements in the answer above to them.
Not sure if this is the answer your looking for but one could be They reacted to it harshly, and were suspicious of all immigrants that came to American from a communist country
