Commerce, trade and exchange make other people more valuable alive than dead, and mean that people try to anticipate what the other guy needs and wants. It engages the mechanisms of reciprocal altruism, as the evolutionary biologists call it, as opposed to raw dominance.
The U. S. Treasury has got borrowing costs like nobody else has. They can borrow basically unlimited amounts. They can stay there for years and years. These assets will be worth more money over time.