Smithsonian put together a solid list of the history of the expansion of the United States, from 13 colonies to a nation spanning the North American Continent and reaching out across the Pacific Ocean.
Eminently usable in class, I think. My only concern: It should also include the annexation of Hawaii in 1898, and the acquisition of territories from the Spanish-American War that same year, including especially Puerto Rico. Expand it to a dozen, and it’s a great list for study in U.S. history, and it contains some surprises.
How much do you know about the Greenland Proffer?
Millard Fillmore's Bathtub 