I think that the bottom two spaces are also a reference to the Spanish Empire. They simply didn't want to write "Spanish Empire" three times.
And Yeah, very good point about the British Empire not being there even though it should be!
Do you think that the US would have been better off had Grover won reelection in 1888 instead of 1892? Also, if you're curious, Grover vetoed a literacy test for immigrants shortly before he left office in 1897.