As any sci fi geek can tell you Battlefield Earth started as a book by L Ron Hubbard. It details the struggle of Jonnie Goodboy Tyler against the alien oppressors the Psychlos in the year 3000. He is captured by a Psychlo named Terl to mine for gold in an irridated area as radiation will explode when exposed to Psychlo breathe-gas.
Naturally Jonnie turns the tables on Terl and in the course of about 1200 pages (and an astronomical number of exclamation points) ends up ruling the universe. A literary triumph!
Of course these Battlefield Earth t-shirts are not from the book but rather from the movie made by famed Scientologist John Travolta. It was pretty much a dismal failure both critically and commercially and earned eight Golden Raspberries. Naturally it has morphed into a "so bad it's good" cult classic and any true nerd wanting to show his or her cred will definitely sport one of these great Battlefield Earth t-shirts in sizes all the way up to 6XL.