If that rule had been in place in 2001, the world would probably look a lot different today.
Imagine if the American military had gone into Afghanistan, helped toss out the Taliban, and then made its top priority wiping out al-Qaeda and subduing the warlords while establishing a functional government in Kabul backed by an Afghan army genuinely capable of defending the country.
That might have happened if the US had a "one war" rule, you only launch one war at a time. You don't launch a second war until you've wrapped up the first. That would also leave you with the capability to fight a second war if one was thrust on you by another country.
A "one war" rule is especially important today when the electorate is increasingly unwilling to support protracted campaigns. You have to finish what you start before you exhaust that essential public support. "No dessert unless you eat your vegetables" - we get taught that by our moms.
Canada didn't go along with the Iraq folly. That's as much because Harpo wasn't prime minister as because Chretien was. We didn't go to Iraq so we won't have to bail out like just about every other country, save Australia, is doing. But that doesn't mean we're not paying the price for the White House ignoring the "one war" rule.
al-Qaeda probably could have been wiped out in 2001 but now its resurgent and, worse, decentralized throughout the Muslim world and even into our own. Bush has played into bin Laden's hands from the moment he decided to invade Iraq, an astonishing combination of hubris and abject stupidity. So now we're still faced with the threat of al-Qaeda and the Salafist and Jihadist spin-offs it has spawned.
We're paying for Bush's folly in still being stuck in Afghanistan, bracing ourselves for combat with a resurgent Taliban. We've been there for five years, plenty of time to establish a functional government and (with a lot of effort and commitment) produce a functioning army and security service capable of defending that government and the country.
Plenty of time indeed. Boosters of the war point to genuine progress that we've made and there has been progress. That'd be great if only the other side, the bad guys, hadn't made so damned much progress themselves. The drug lords have made progress. The warlords have made progress. The Taliban is resurgent and Pakistan has become quietly defiant. By all accounts, their progress far outstrips ours. There's the problem.
We've squandered the one thing we have the least of and need the most - time. This thing was supposed to be over long ago. Hillier told us we were just going over there to kill a few dozen "scumbags" in Kandahar and we've killed many dozen already and there are more coming our way.
There are alarms going off that a failure in Afghanistan will mean the end of NATO. If it does it's because key members - Germany and France (sort of) - have decided they would prefer a more rational alliance, one among the European Union membership, one that isn't going to be America's foreign legion. Don't forget that Bush tried very hard to cajole NATO into jumping into Iraq also. No, George Bush has lost the confidence of the other NATO leaders save, of course, for our own.
Imagine where we might be today if we'd only started this millenium with a "one war" rule.