Why wouldn’t every country (or most) have a military? Looking around it seems like the west is the only part of the world community where some tinpot leader doesn’t arise every ten years or so and start eyeballing his neighbors’ property. Heck, it was only sixty years ago that the west had a couple of crackpots eyeing (and running over) their neighbors and it was just a little over ten years ago that Europe got to stop worrying about the Soviets. Overall lesson of world history is that if you don’t have an army that can hang with your neighbors natural selection kicks in and your country may go the way of the dodo, and nowadays that means a standing army.
And even if your neighbors are all friendly, having a strong military is a powerful political tool. Setting aside decades of sanctions for a moment, it does seem that the invasion of Iraq helped motivate Libya to end its nuclear weapos program (not that that justifies the invasion of Iraq in my mind, however).
Also, depending upon how developed a country is, having a military force that can be projected globally can be a political necessity or at least a good idea diplomatically. Japan was criticized for not helping more in Gulf War I and (IIRC) Afghanistan and so has sent troops into Iraq for this go-around. The fact that their constitution forbids them from entering into combat on foreign soil has not deterred their detractors. Another example, using Japan again, of having a military being politically a good idea is that after WWII Japan’s constitution forbade them from having a standing military, but the U.S. persuaded them to alter it to allow them a defense force in the hopes that it would help keep communist forces in check in the Pacific region.
Then there’s the question of self-respect. As in “What self-respecting country doesn’t have a military?” Not saying that that’s a good reason to have a military, but I can easily imagine that not looking like a pansy to themselves or their neighbors can be a pretty strong motivation.
Finally there’s the good old keeping the peace reason. Kinda hard to fight off a rebellion if you don’t have an army.
In spite of all that there are at least a few good reasons not to have a military, and all you have to do is look at Haiti for a primo example:
Although they still have a military on paper, every branch of it has been demobilized because they threw their President (Jean-Bertrand Aristide) out of office in the early nineties. He regained office in 2001 and one of the first things he did was shut down the military so they couldn’t challenge him again. Fat lot of good it did him though; Haiti currently has a rebellion on its hands and I’ll give you three guesses as to who the leaders of it are.
Lobsang, I checked dictionary.com, the OED, and Oxford’s Dictionary of Politics, and none of them stated what you said. However the ODP didn’t even have a definition of country in it so I went with nation-state instead. Hope that helps.