If Americans stopped living beyond their means, the American economy would collapse.
If the American economy collapsed, it would severely shake the world economy.
Don't believe for a minute they couldn't live without us, or that we couldn't learn to live without ourselves, but it wouldn't be much fun, especially if it happened abruptly. What follows the present era of over-consumption will of necessity be more judicious, because all the easy stuff will have been sucked up.
People live beyond their means because they sense that life is short. The method fails them when they live longer than they expected.
"If I'd known I was going to live this long I would have taken better care of myself."