I've been contacted many times over the last few weeks by folks asking where they can find websites to help in their research. FamilySearch has a fairly good index to useful sites by topic. Most of us haven't thought to look for it there but rather focus on the IGI, Pedigree Resource File and Ancestral File data.
Here's the link to the 'Browse Web Sites'. From here you can drill down by subject.
As an example, you want to know where the boundaries between the 48 states were at a given point in time. Look at Land and Property. Choose the United States. Click on 'Boundaries of the Contiguous United States' and watch the animated map show the boundary lines appear starting with 1650 and continuing on to today. Now you can see why your great grandparents are found in Alabama, but they actually lived in what we now know as Mississippi.
Two more webpages arranged by topic are found on the Family Genealogy and History Internet Education Directory and the Regional Genealogy and Local History Research pages.
Hopefully, you will find some information from these links to help in your own family history research