Joseph Stalin once famously quipped: "The Pope! How many divisions has he got?"
Technically speaking, the pope IS a secular ruler of a country that holds an observer status at the UN, and as far as I'm aware, has a standing military (Swiss guard mercenaries).
The Popes of the past clearly had a lot of military power and participated in and started tons of wars (most notably, several Crusades).
As such, can Vatican (or Pope) legally declare war in 2013?
The answer should be based on actual Vatican/Catholic Church legal rulings or official statements.
The question does NOT pertain to whether Catholic doctrine views the idea of declaring war positively.