Re: the names
BTW the correct name for the cartridge is the 9mm Parabellum. The origin of the other names requires a brief history lesson.
The cartridge was originally developed by the German gun and ammo manufacturer DWM for its Pistole Parabellum, which had been designed by their engineer Georg Luger as an improvement of the earlier Borschardt pistol. "Para bellum" means "for war" and is derived from the ancient Roman saying "Si vis pacem, para bellum", which is usually translated as "If you want peace, prepare for war". By late 19th century standards, the Parabellum was a relatively large and powerful handgun, so DWM primarily marketed it as a military sidearm with commercial sales as an afterthought. Therefore, the name Parabellum was thought to be very appropriate.
Despite the pistol's official name, the Luger name remained commonly associated with the design. When A.F. Stoeger became DWM's official U.S. distributor following WWI, they wisely perceived that American buyers might have trouble with the name Parabellum, so they marketed the pistol as the "Luger". Since this was basically the only gun available in America prior to the end of WWII that fired the 9mm cartridge, it was logical to call the round "9mm Luger" to prevent confusion. Although the Luger pistol was very expensive and never sold particularly well in the USA, the name stuck. (Most Luger pistols in America today are either German WWII G.I. bringbacks or European military and police surplus brought in by postwar importers; the original Stoeger imports are actually quite rare and sought after.)
The other names such as 9x19mm are usually intended to prevent confusion with other 9mm rounds, most commonly .380ACP, which is known as the 9mm Browning Short or 9x17mm in Europe. "Short" is commonly translated into the local language of the ammo or pistol manufacturer, most commonly "Kurz" in German or "Corto" in Italian or Spanish; e.g. Italian-made Fiocchi ammo is headstamped "9mmBr.C." for "9mm Browning Corto". Other less common but still prevalent European 9mm rounds are the 9x20mm Browning Long and 9x23mm Largo.
[EDIT: I notice that Jim Watson beat me to some of this.
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