Try this scenario on for size.It's World War II. You're a Korean citizen. Which doesn't matter to your neighboring country, because Japan needs soldiers. So they 'recruit' you and send you into battle in Manchuria -- where you promptly get captured.
However, your captors are in need of soldiers. So they 'recruit' you into the Red Army and send you out again -- where you're captured by the Soviets. Welcome to the hammer and sickle, comrade: grab a rifle and go shoot some Nazis -- who capture you first and, as they were wont to do, impress you into their army, sending you off to Africa so you can shoot some Allies.
Only the Allies capture you first. And recruit you.
So you're sent to Italy, working with the British -- not so fast. Guess who grabbed you this time? The Italians. But don't worry, because the Americans got you about five seconds later. At this point, it's probably safe to say you want to shoot something, so they give you the opportunity. Hello, G.I. Joe. And as an American soldier, you -- stabilize, staying one through the end of the war.
http://tvtropes.org/pmwiki/pmwiki.php/Main/EnemyExchangeProgram
This is typically a video game trope, one which comes into effect when you can either capture or manufacture enemy units and make them fight on your side. Starcraft players know it well as 'I'm going to use mind control on that Drone...' -- and if you're careful and have the resources, you can recreate the entire Zerg tech tree and have your own colony battling alongside the Protoss forces.
But when it gets into real life, it's still about taking the enemy's things and putting them to work for you -- including their soldiers. As demonstrated above.
Now. How are you going to apply for your armed forces pension?