I could be wrong, but I always interpreted that scene as Michael telling Kay how senators and presidents can have their enemies killed just a like a Mafia Don. I don't believe Michael was talking about sending men off to war fighting America's enemies. I believe he is referring to senators and presidents killing off their personal/political enemies.
You probably are right that Michael believed that senators and presidents have their enemies killed. I think he may have broadened it to mean sending men to war to make it plain to Kay.
