We started American history this year too. I bought Stories of Amercica, and I am adding whatever I like with it. I bought a great reference book for history called All Through The Ages and it has listed by grades which books are the best for which time periods. I HIGHLY recommend it if you want to know what to supplement with but don’t have much time to sort through all the books out there.
Today, we finished John Cabot (which is not in Stories of America). I didn’t want to skip him, so I briefly touched on him, in addition to Magellan. My kids have enjoyed learning about explorers and I didn’t want to pass it by too quickly. I used a few of the books mentioned in All Through The Ages for this study.
Does this help?