A lot of debt also arises because of savings needs. If everyone is saving for retirement, for example, that savings has to be debt marked somewhere else. Examples:

* Social security used to have a huge surplus, that was savings that had to go somewhere (even if it was just a savings account in a bank, the bank would then be able to lend it out). They instead buy treasuries and that savings becomes debt to the USG.

* China likewise needs to save dollars because it doesn't want them sloshing around in their economy leading to inflation, so instead of using it to buy things they buy treasuries, and their savings becomes debt to the USG (not always a great deal for China if interest rates are below inflation).

The dollar has been so useful in the past as a currency of trade because you could save large amounts of it easily by buying US treasuries. One reason China doesn't want the RMB to be used so heavily for trade is that they don't want to do the same yet.

Actually it kind of is, in as much as it expands the money supply.

When a bank issues debt, the money is created 'out of thin air'. When the debt is paid off, that money is destroyed. However usually more debt is being created than redeemed as things go on, so the total money supply increases (this is a good thing, as it allows the economy to expand).

Various regulations and central bank market interventions (quantitative tightening/easing) control this process, which thus can be induced to 'print money' if the government wishes - assuming they have a sovereign currency.