Offer your thoughts or opinion on the input financial query or topic using your financial background.

Where do countries / national governments borrow money from? 
Sovereign states borrow money explicitly in a two primary ways: A sovereign cannot be compelled to repay debt, and there isn't a judicial process like bankruptcy to erase debt. When sovereigns default, they negotiate new terms with creditors and pay back some fraction of the actual debt owed.  They can also print money to repay debt, which has other nasty consequences. But, while a state cannot be compelled to repay a debt, creditors cannot be compelled to loan money to the state either! Any enterprise of sufficient size needs access to capital via loans to meet daily obligations in anticipation of revenue -- even when times are good. Defaulting makes borrowing impossible or expensive, and is avoided. Regarding using your military to avoid repaying debt... remember what Napoleon said: "An army travels on its stomach". Military campaigns are expensive... no borrowing ability means the soldiers don't get paid and the food, fuel and ammo don't get delivered. Smaller countries have other risks as well. Many nations are essentially forced to use US Dollars as a reserve currency, or are forced by the market to borrow money in a foreign currency. This creates a situation where any risk of non-payment results in a deep devaluation of the local currency. When your debt is denominated in dollars, these shifts can dramatically increase your debt obligations from a local currency point of view. You also run the risk that a larger or richer company will park warships in your harbor and seize assets as payment -- the US and Britain engaged in this several times during the 19th and 20th centuries. In general, not paying the bills has a cascading effect. Bad situations get worse, and they do so quickly.