As T. E. Lawrence famously described it, fighting rebels is "like eating soup with a knife." Guerrillas do not depend on vulnerable lines of supply and communication, so counterinsurgents must target them directly, and even a few thousand armed guerrillas can create chaos in a country of tens of millions. Guerrillas camouflage themselves among the population; frequently the only way to distinguish an insurgent from a civilian is when he (or she) opens fire.
This is why the history of counterinsurgency warfare is a tale of failure. Since World War II, powerful armies have fought seven major counterinsurgency wars: France in Indochina from 1945 to 1954, the British in Malaya from 1948 to 1960, the French in Algeria in the 1950's, the United States in Vietnam, the Soviet Union in Afghanistan, Israel in the occupied territories and Russia in Chechnya. Of these seven, four were outright failures, two grind on with little hope of success, and only one - the British effort in Malaya - was a clear success.
Many counterinsurgency theorists have tried to model operations on the British effort in Malaya, particularly the emphasis on winning hearts and minds of the local population through public improvements. They have not succeeded. Victory in Malaysia, it appears in retrospect, had less to do with British tactical innovations than with the weaknesses and isolation of the insurgents. The guerrillas were not ethnic Malays; they were recruited almost exclusively from an isolated group of Chinese refugees. The guerrillas never gained the support of a sizable share of the Malaysians. Nevertheless, it took the British 12 years to defeat them, and London ended up granting independence to the colony in the midst of the rebellion.
Paradoxically, it is only some weaker countries that have succeeded in suppressing rebellions, albeit by unleashing tremendous brutality against the civilian population. This is the approach that Guatemala adopted in the late 1970's and early 1980's to crush a growing communist insurgency in the countryside. Villages were wiped out in a campaign that killed about 200,000 people and made an equal number refugees. Hafez al-Assad of Syria succeeded with a similarly murderous approach when he crushed the Muslim Brotherhood rebellion in 1982, as did Saddam Hussein when he defeated the Shiite uprising in southern Iraq after the Persian Gulf war in 1991...The fact that we must consider them underscores the caution that should be employed before deciding to go to war. Still, given where we stand today, if the United States can find a way to withdraw most of its troops over the next several years and leave behind an Iraq that is not in a civil war, that is not a haven for Al Qaeda and is not an immediate threat to its neighbors, history may well record it as an odds-defying success.
I wouldn't bet the farm on it.