Interesting article by Stephen M. Walt in Foreign Policy regarding how different the world would be if we had a Realist at the helm of policy rather than a neoconservative or liberal interventionist (flip sides of the same coin. though one could argue that a Neoconservative is a Liberal Interventionist with more bloodlust and less aptitude with math). As you might remember, Stephen M. Walt was the scholar who got in all kinds of trouble with AIPAC after having the temerity (along with John Mearsheimer) to make the very obvious observation that our current Israel policy is extremely detrimental to American interests (and some would argue Israel's).
Here are the first two differences:
#1. No war in Iraq. This one is easy. Realists like Brent Scowcroft played key roles in the first Bush administration, which declined to "go to Baghdad" in 1991 because they understood what a costly quagmire it would be. Realists were in the forefront of opposition to the war in 2003, and our warnings look strikingly prescient, especially when compared to the neocons' confident pre-war forecasts. If realists had been in charge, more than 4,500 Americans would be alive today, more than 30,000 soldiers would not have been wounded, and the country would have saved more than a trillion dollars, which would come in handy these days. Hundreds of thousands of Iraqis would still be alive too, and the balance of power in the Gulf would be more compatible with U.S. interests.
#2: No "Global War on Terror." If realists had been in charge after 9/11, they would have launched a focused effort to destroy al Qaeda. Realists backed the war against the Taliban in Afghanistan, and a realist approach to the post-9/11 threat environment would have focused laser-like on al Qaeda and other terrorist groups that were a direct threat to the United States. But realists would have treated them like criminals rather than as "enemy combatants" and would not have identified all terrorist groups as enemies of the United States. And as noted above, realists would not have included "rogue states" like Iran, Iraq, and North Korea (the infamous "axis of evil") in the broader "war on terror." Needless to say, with realists in charge, the infamous 2002 National Security Strategy calling for preventive war would never have been written.