Browning HP with 21 rd mags, fully loaded with nasty hollow points. The only kind of war I'd be dragged into would be one of civil unrest, so to Hades with FMJs.
I'd probably chose a HK45 above all others, but I'm still working on getting one of those....
Glock 19...high capacity, good ergonomics (not great, but good), easy to carry and hide if necessary, accurate and uber-reliable. Even loaded with FMJ it can put a lot of rounds on target quickly and accurately.
That said, I wouldn't "go to war" with any pistol - I'd bring my rifle and all my friends with thier rifles...
Are you referring to being called up in a draft to fight a war somewhere? If so, I would want a Beretta 92fs. There should be an ample supply of 9mm ammunition and repair of the weapon if necessary in theatre.
Out of what I own?
1911 is what I shoot the best, and I like .45ACP...
M9A1 has a light, which might be nice, and double the capacity...
Decisions, decisions...
(1911 wins, because if I'm down to my pistol in this here "war," I want something I can shoot well in a hurry and has lots of "oomph" behind each chunk of metal.)
My SW 3913, the single most reliable gun I own. Big enough to shoot comfortably and accurately out to moderate distance yet small enough to easily hide if need be. Not the highest capacity gun I own but I have 10 mags for it and 9mm ammo is everywhere. Hell, you can even get it at gas staions in some rural areas.
One of my Sig P220's in .45 or any of the 1911's in the safe due to stopping power. If ammo and repair were sole concerns my Beretta 92 would have to suffice. Like many others these would all be secondary to a good battle rife. That decision would be a quandry in itself, so many to choose from.
There are plenty of guns I would trust my life to. Browning Hi-Power, 1911, Glock, Beretta, Sig, S&W revolvers... The list goes on. Just don't send ms out there with a 1895 Nagant or a 32 KelTec.