Almost all the firearms in White House Down are chambered for 9mm.
Georg Luger developed the 9×19mm Parabellum cartridge from his earlier 7.65×21mm Parabellum round. Luger had derived the 7.65×21mm Parabellum from the original 7.65×25mm Borchardt cartridge in his efforts to improve upon the Borchardt C-93 pistol. Shortening the length of the cartridge case allowed him to improve the design of the toggle lock and to incorporate a smaller, angled grip. The initial 9×19mm Parabellum cartridge was created by removing the bottleneck of the 7.65×21mm Parabellum Luger cartridge, resulting in a tapered rimless cartridge.
The name Parabellum is derived from the Latin: "Si vis pacem, para bellum" ("If you seek peace, prepare for war"). The cartridge is known as "9mm Luger" to differentiate it from the 9x18mm Makarov and 9mm Browning Short (better known as .380 ACP) cartridges. It was introduced in 1901 and has been used by most major militaries in the world for over a century, although .45 ACP is more favored by serious shooters for its larger exit wounds and stopping power. Despite this prejudice against the cartridge, it has stood the test of time and proved to be quite popular as a self-contained pistol round that is used by military and police all over the world, mainly because it is cheaper and more available than the .45 ACP cartridge.
According to the 2006 edition of Cartridges of the World, the 9×19mm Parabellum is "the world's most popular and widely used military handgun cartridge." In addition to being used by over 60% of police in the U.S., Newsweek credits 9×19mm Parabellum pistol sales with making semi-automatic pistols more popular than revolvers. The popularity of this cartridge can be attributed to the widely held conviction that it is effective in police and self-defense use. Its low cost and wide availability are self-sustaining contributors to the caliber's continuing popularity.