Georg Luger developed the German pistol named after himself and the cartridge in 1902, hence the 9mm Luger. Mr. Luger probably didn't realize he developed the most practical centerfire cartridge for handguns.
It's practical because of its low cost, selection, and availability. I can order ammo online or go to the neighborhood Wal-Mart to pick up some Winchester White Box and pay less than any other centerfire cartridge.
Parabellum is derived from the Latin saying Si vis pacem, para bellum when translated means, "If you seek peace, prepare for war".
The 9mm cartridge has been tested and proven to have enough stopping power. People who say they wouldn't carry a 9mm because it doesn't have enough stopping power probably have never been shot and never have shot anyone. If you have done either than why are you reading this blog? The whole argument is like arguing why a 6 cylinder car is better than a 4 cylinder car. Or why a 60" screen TV is better than a 48". There are advantages and disadvantages to either side.
I own several different handguns, most are chambered in 9mm. I like this particular cartridge because it's one of the cheapest and easily accessible type of ammo. The more ammo I can buy means the more practice I can get and that leads to better shot placement. Another advantage to the 9mm is the manageable recoil. Even sub-compacts chambered in 9mm are easily controlled with just a little practice.