Re the Vatican's Swiss Guard:

"Swiss mercenaries who fought in various European armies from the 15th cent. until the 19th cent. These mercenaries, who were not volunteers, were put at the disposal of foreign powers by treaties (called capitulations) between the Swiss diet, the separate cantons, and the foreign power concerned, in return for money payments.

The Swiss constitution of 1874 forbade all military capitulations and recruitment of Swiss by foreign powers, although volunteering in foreign armies continued until absolutely prohibited in 1927.

An exception to the ruling of 1874 is the Swiss Guard of the Vatican, founded in 1505 by Pope Julius II, which is the personal guard of the pope."

Story goes that they won their fearsome reputation by killing more in battle than any other troops at that time - mainly due to their discipline, tactics and weapons - they tended to cause serious/fatal head wounds. Previously the bulk of those killed in battle died as a result of wounds received, i.e., not killed outright. Julius II needed troops he could trust for his own protection and hired the best available at the time. But the truth remains that the Vatican's Swiss Guard remain a mercenary force and have nothing whatsoever to do with the conscript Swiss Army - of knife fame.