Why did so many american indians die as a result of european disease?

Because the Native Americans were not introduced to European diseases on their own homeland.
Their immune systems were exposed to European Diseases that they never were in contact with before, which caused sickness. Without today's medicine, they were basically helpless and left to die from the exposed diseases.

The  pan-african movement  was an "emotional, cultural, psychological and ideological  movement  that began among the  african  dispora in the western hemisphere, for a closer  purpose, so that  african  people could feel secure, attain political, economic as well as psychological power visa vis other races or world regions" .