I think they can keep printing money for many years and major conflicts like against islamic state for example, only help the economy. As many countries owe money to the US as US owes to them, so in the end the national debt is kind of balanced.
you have no idea what your talking about.
http://www.bea.gov/newsreleases/international/intinv/intinvnewsrelease.htm"The U.S. net international investment position at the end of the second quarter of 2014 was -$5,445.1 billion (preliminary) as the value of U.S. liabilities exceeded the value of U.S. assets (chart 1, table 1)."
America is a net debtor and owes the world 5.4 trillion dollars.
not only that but it continues to only get worse, America has a trade deficit of about 40 billion $ a month with the rest of the world
http://www.tradingeconomics.com/united-states/balance-of-tradeif no one agrees to loan the money, America can't pay for its imports anymore.