I figure most eras of American history have their share of hubris but I would stack the first decade of the 21st century up against the best of them:
2000 - Karl Rove finds the perfect candidate for President through whose administration he will be able to manipulate the political system and create a Permanent Republican Majority. Instead, the tenure of George W Bush sinks into crass opportunism, abuse of power and executive incompetence that results in record deficits, a tarnished image and a set back to conservatism that may require a generation to overcome.
2001-2003 - Donald Rumsfeld and the neo-conservatives decide that, with a couple of bombers and Army Rangers, they can scare the regime in Iraq into (American) bloodless submission. Then all the petroleum producing countries in the region would lay their oil at our feet and marry their sons to Israeli princesses. "Democracy" and Pax Americana would flower in the Middle East and through out the world. Instead Iraq is destroyed, the price of oil spikes, the military is straining at the seams and Iran emerges as a serious regional power.
2000-2008 - I love this one: the financial geniuses on Wall Street come up with formulas that allow them to structure their portfolios such that risk can be managed while returns continue unabated. Got that? Risk Will No Longer Be A Problem! The result? A complete financial meltdown.
Gotta love it!