Embattled empires through the ages suffer an arrogance that drives them to plunge ever deeper into military misadventures until defeat becomes debacle. In 413 BCE, a weakened Athens sent 200 ships to be slaughtered in Sicily. In 1921, a dying imperial Spain dispatched 20,000 soldiers to be massacred by Berber guerrillas in Morocco. In 1956, a fading British Empire destroyed its prestige by attacking Suez. And in 2001 and 2003, the US occupied Afghanistan and invaded Iraq. With the hubris that marks empires over the millennia, Washington has increased its troops in Afghanistan to 100,000, expanded the war into Pakistan, and extended its commitment to 2014 and beyond, courting disasters large and small in this guerilla-infested, nuclear-armed graveyard of empires.
In addition to the above, reigning powers also wage war on one another. Some people think the British Empire faded quietly into the night. What are they drinking? Two global wars broke the back of the Empire, with a new hegemon emerging. Those 2 wars cost nearly 100 million dead. Add to that the maimed and the families of the dead and maimed - by any measure, that's a noisy exit from world domination.