The US Federal Government on Sunday 30th Sept 2013, at midnight, had to shut down, unable to agree the federal budget. The reason being, the government literally has run out of money, it was unable to borrow any more, as it had reached the legal debt ceiling.
The US has a huge national debt, caused by a simple fact, that the US government spends more than it earns in taxes. It runs a budget deficit.
Thus to bridge that gap, the US government borrows, it issues T-Bonds (Treasury Bond).
What is the US National Debt ?
A good site:
As you can see, over $16 trillion.
[$1000 Million = $1 Billion]
[$1000 Billion = $1 Trillion]
US National Debt is $16.9 Trillion = £10.5 Trillion
US 2012 GDP was $15.68 Trillion = £9.74 Trillion
Thus Debt / to GDP Ratio is 108%
These numbers are incredible.