What are some changes and continuities in the demography of North America from 600-1750?
There is not written history for most of that time span.
Read widely and take good notes ... and MAKE SURE YOU DON'T SIMPLY COPY FROM ANY OF THESE WEBPAGES:
http://www.google.com/search?q=north+america+600-1750&oq=north+america+600-1750&aqs=chrome.0.57j62.8756&sourceid=chrome&ie=UTF-8