Before this incident, zombies had been used for heavy manual work throughout the United States; their slow speed and limited intelligence were acceptable in light of their cost-free labor. After the Big Bubble burst, down-and-out people, with no other prospects, became zombies to escape sadness and pain.
However, zombies were not the only living dead creatures found in the country. Vampires arrived in the U.S. at the turn of the 20th century and spread their curse. Unlike zombies, vampires were able to retain their intelligence, and were able to grow their numbers by occasionally convincing the living that vampirism was a path to equality in a "brotherhood of blood".
The exact cause of the Riots of 1934 was unclear, but rumor had it that vampires had to some extent reawakened basic human desires in zombies. In June, 1934, the zombies of Denver, primarily working the stockyards, suddenly rebelled. The renewed purpose seemed to improve zombie mobility, and then began killing every living person they could find. Moreover, it created a sort of bloodlust in them, as zombies often chewed on or outright ate their victims. Moving en masse, the zombies made their way to the heart of Denver.
The riots raged for a night. The Army dispatched overwhelming force, and made liberal use of flamethrowers on the zombies. Moreover, the authorities began clamping down on vampires, as well. Fortunately, the riots did not spread outside of Denver.
Roughly four days after the initial outbreak, the authorities had destroyed enough zombies and vampires that things had calmed down, and the roads through Denver were opened up again, although the authorities were still patrolling the city and maintained check points. The city itself was badly damaged by the violence.