I found the following animated geographic history of the USA enlightening. Most of the historical events I was at least vaguely aware of from movies and reading but this really brought the picture together for me. The website seems to use a somewhat dated interface that is a bit clunky but none the less it works well enough.
Click the picture above to load the page. Then close the advertisement overlay by clicking the cross at it’s top left corner. Press play. All up it takes about ten minutes to watch.