James Joyner makes an interesting point today:
As we approach the tenth anniversary of the American invasion of Iraq on March 20, it's worth reflecting on the fact that it has been nearly seventy years since America's last successful major war.
On August 15, 1945, known as Victory Over Japan Day or V-J Day, the Japanese unconditionally surrendered, marking the end of the Second World War and establishing the United States as a superpower. Since that day, the United States has lost three major wars—Korea, Vietnam, and Iraq—and is counting down the months until its loss in Afghanistan.
James doesn't count the Gulf War as a major conflict, and doesn't count the Cold War since it wasn't fundamentally a military conflict. Those are both pretty defensible judgments.
So what do all these unsuccessful wars have in common? I'd focus on one thing: none of them were ever intended to be major wars. They just growed like Topsy, so to speak. Conversely, the U.S. has arguably been successful in plenty of wars that were meant to be small and really did stay small: the Dominican Republic, Grenada, Panama, Kosovo, Libya, etc.
So there's your lesson: if you plan for a small war, be damn sure that it's going to stay small. If it might not, then plan for a big war. If that's unacceptable, don't go to war. That's the bare minimum lesson, anyway.