Code Name Z for Zombie
The 1936 film, Revolt of the Zombies tells the tale of a Cambodian monk who uses a spell to raise a regiment of zombie troops. He commands them as mercenaries to WWI France where the French generals hire them for the front. No sooner deployed and sent over the top, the zombies overwhelm Austrian positions to score a victory for the French and payday for their master. As you might guess, though the zombies are impervious to machine gun fire, they make for highly unreliable units. They soon tire of their overlords and return to the ranks as an enraged lynchmob bent on payback.
A variation on the theme is spun by Joe Dante in his Showtime series*, Homecoming. The irate Iraq War fallen burst out of their coffins on Election Day to stagger to the voting booth to turn the President out of office--the man who sent them to die for a dodgy dossier. And God help anyone who stands in their way!
Mind you, that's awfully affirming of democracy on the part of the undead, especially when they could simply settle the score by ripping the heads off the Prez, the Veep, the SecDef and Congress.
*Also submitted as an entry at the Turin Film Festival