Those were the
Haradrim, Men of the East, who served Sauron. The beasts were called
oliphaunts, and were a corrupt version of elephants bred for war.
Funny, I always thought, how Tolkien had the Arabs (who are widely recognized as the prototypes for the Haradrim) pegged way back in the '50s.
Beggin' yer pardon, Long Cut, but the Haradrim were from the South...also known as the Southrons.
The company that Frodo, Sam & Gollum saw at the black gate were the Easterlings.