I thought about this question during the height of the Greek economic crisis several years ago. The media was saying that Greece had run out of money, having used funds that had been set aside for a natural disaster, and they really badly needed a loan.
Suppose that during this period, an alien spaceship crash-landed in Greece and the aliens proceeded to invade the country. Since Greece has no money (= cannot buy weapons, ammunition, pay their soldiers, etc), and it cannot borrow (since nobody being willing to lend Greece money was the cause of economic crisis) does it mean Greece will be easily conquered? If the answer is no, where will Greece get the money to defend itself from?
I'm asking this as an economics question, so I'm not thinking of stuff such as whether NATO intervenes or what the technological capabilities of the aliens are.