On a Withdrawal from Iraq

Many claim that a withdrawal from Iraq would be a mistake--that we should stay until we have achieved "success" or can claim some sort of victory. This victory is often defined as our ability to achieve a stable democracy where the Kurds, and Sunni and Shiite Arabs coexist in harmony, and the country becomes a U.S. ally. However, is this achievable in any realistic time frame?
Let's first look at Northern Ireland; it has taken nearly 100 years for the opposing populations, Catholic and Protestant, to approach a period of cooperation and mutual respect, and this is in a situation where one of the contestants did not view Britain as an occupying power, and everyone spoke the same language and had a common heritage.
Now, let's look at Iraq. Sunni and Shiite Muslims split apart in the seventh century after Christ over the question of kingship. In other words, there has been division and violence for some 1400 years now between the current warring factions in Iraq. Furthermore, unfortunately, these enemies have not infrequently used terrorist tactics against each other. In 1090 AD, a fanatic group of Shiites named themselves the Assassins of Alamut, and made a name for themselves by the unstinting use of assassination as a weapon against their Shiite enemies. This is the origination of the English word assassinate or assassin.
Now are we supposed to believe that our military forces, as marvelous as they are at jobs within their scope, can somehow magically bring Sunnis and Shiites together within a few years--that 1400 years of violence, extremism and, sometimes, fanaticism can be completely resolved by our military within such a short time frame? This is what President Bush has been promising for 5 years now and John McCain continues to promise. However, no occupying power, no matter how professional and well-trained, can make friends out of bitter enemies.
No one can predict for sure how our leaving Iraq will affect that country. Hoards of conservatives warned of dire consequences of our leaving Vietnam; it would be another falling domino in the unstoppable wave of communism. Despite such warnings, our leaders summoned the will to leave, and nothing happened. Communism was stopped; we are currently at peace with Vietnam. Again, no one can say exactly what the cost of leaving Iraq will be, but I can tell you what the war is costing the country right now: over 4000 American dead--that's 800 a year and counting, an all volunteer military that its own generals state is cracking under the weight of continual deployments, and $400,000,000 per day in expenses to this country. What could we not do with that money right here.
If we were to stay in Iraq for as long as many American military planners estimate it might take to possibly achieve some sort of success, this war would become the single biggest expense in the history of the republic. An expense, I might add, that we are currently passing on entirely to our children due to President bush's tax cuts for the wealthy. Our current definition of success in this war is utterly at odds with the history of the region. The cost of continuing it indefinitely, as Mr. McCain would have us do, is far too high in terms of American lives, American finances and the strains that it places on the best military on the planet.