During the first hundred years of european exploration, what was the main cause of the decline in the number of native americans living in north america?

Disease is the answer I believe... If not than it is death by war or massacre

I am sure the answer is diseases. The white men brought diseases with them when they came to explore North America. 

The second , larger puritan colony of massachusetts bay was conceived as a "city upon a hill". but it also struggled with internal turmoil like the salem witch trials and external conflicts like king philip's (metacom's) war.