However, there are not too many open curriculum (no general education requirements) colleges like Amherst, Brown, and Evergreen State.
At a college with a typical amount of general education requirements, you may have to use 20-30% of your courses on general education (though some schools require more, e.g. nearly 50% at MIT), 35% or so on a history major, and have the rest as free electives, within which you can take additional history courses or courses in any other subject you like (some other subjects like political science, economics, sociology, and statistics can be useful supporting subjects for a history major).