I'm mostly interested in art and historical sites
My friend, however, is more interested in beaches and resorts, so ideally it would be somewhere that can accommodate both the historical and the...beachy aspects!
Sorry for taking so long to reply to your message!
Resort vacations will of course be more concentrated in the south - Florida, the Carolinas - but the Carolinas and Georgia will also be rich in historic sites. So you could plan a couple days at Myrtle Beach (almost entirely resort/shopping) and a couple at Savannah and/or Charleston, for instance.
Virginia Beach (in my state) is perhaps a cheaper stay and smaller selection of resort-ish options, but is a VERY short drive from Colonial Williamsburg, Newport News (Civil War sites and of much military interest), Jamestown, about two hours from Richmond (capitol of the Confederacy, and a beautiful city with excellent food and museums - VMFA
is a particularly fine surprise to many who visit), and three hours from Charlottesville (gorgeous farm country, and seat of Thomas Jefferson's Monticello and the University of Virginia.
Farther north, there are still beach options and also increasing shopping and cultural opportunities with theaters going from country music-style showcases in Myrtle Beach, to Broadway and the like in New York and Boston. Historic sites are more concentrated, and the Blue Ridge Parkway offers great beauty along a route favored by drivers, cyclists, and hikers alike. In Philadelphia and Boston, historical interest shifts from Southern Civil War points of interest more into Revolutionary and Colonial sites, dating back to Salem Village and the earliest European settlements.
Along the entire coast, as you may notice, historical sites concentrate most on European and American interest, with Native American history more marginalized. History predating the 17th century can be found, but it's harder to find and is often a sort of adjunct to American focus. Jamestown has blended its presentation far better than it was presented when I was a kid 40 years ago, but there's no escaping the balance. The farther West you go in the lower 48, the more you can find native sites and focus.
Every state and all the major historical and tourist sites will have online resources, so it's easy to really custom tailor a vacation to your curiosity and the time you have available. Hooray for Teh Intarwebs!