Coming Home To Roost ;Of Chickens, Overextended Empires and Teachable moments

The proverbial chickens are coming home to roost in Iraq. The ISIS, the Islamic Army of Iraq @ Syria, or whatever, is already in control of two of the country's largest cities, Mosul and Tikrit,and how much longer until it overruns Baghdad, throws out the puppet government of the United States, and and initiates a regime of conservative religious repression that will make the Taliban look like the ACLU. Is this a teachable moment for America? Are such moments any longer possible? How do we say "the perils and pitfalls of empire?" It happened to the ancient Romans,it happened to the medieval mongols,and it happened to the rather modern English. Pride, greed, and overextension, caused by a shortsighted inability to understand that the more one invests, the more one risks. If you intend to expend great amounts of resources controlling large parts of the world, you had better be sure to include a rock solid, fail safe scheme for reaping even greater resources from controlled (aka conquered, colonized, occupied) areas, which invariable proves difficult, if not impossible, though heaven knows they all (all the great empires) try hard. Alas, someday we may learn to leave well enough alone.