I am appalled at the amount of information left out of my child's history curriculum.?

There is very limited mention of the motivations behind the Native American conflict, limited African American history, and very little international discussion. I understand that in the 4th grade, you must be careful what you teach your children and how much they can absorb, but I really feel that my son is able to grasp simple concepts that would branch out his thinking. We discussed MLK day and what had happened during that time and he was enthralled by this time period. Is there any way to purchase supplements for grade-school children to teach them about the broader events and cultures in the world? I can't seem to find anything that would be age-appropriate and I am desperate to educate him more throroughly at home since it is apparent our education system will not. Thanks for any ideas!