This group of Banana peels who worshipped a loser weren't very grand or really much of an army. They were formed by Bananaskin Groundhopper, and the only claim to fame they had was their defeat at the hands of Cookie Monster, whose eviltude is known throughout the universe. Their only victory was against Cassus Fett the Lesser, a Cassus Fett wannabe who wanted to be an ancestor of the Boba Fett. The battle consisted of Cassus leaving a biker bar and slipping on the Grand Army of Banana Peels before falling into a giant cheese grater. And no, you don't want to know what happened afterwards.
They were discovered by the Loser Darth Bob, who recruited them in his attempt to destroy Darth Darth Binks. He failed horribly, and the Banana's sided with Binks who sent them off to explore the unknown's of the universe in a flying dishwasher. Why he did this is uncertain.
The Grand Army of Banana Peels encountered KHAAAN!!!, an insane psychopathic Mega Supah Dupah Sith Overlord. He hired them to man his mighty fleet of dirigibles and set out for the moon of Endor. They were instrumental to the establishment of KHAAAAAAAN'S!!! Ewok Burger Patties, a fast food chain. However, the slightly annoyed locals popped the dirigibles with their sticks, stranding the Grand Army of Banana Peels on the surface. After the PWNing of the Ewoks, KHAAAAAAAN!!! let them go where they pleased and set off on his ill fated quest for a more profitable fast food chain.
The Grand Army was destroyed when a mysterious being devoured them. Why is uncertain, but he was never seen again. Until he attacked New York.
So ends the Grand Tale of the Grand Army of the Banana Peels, whose really Grand Existence really wasn't that Grand at all.