The USA has never seemed hindered by the alleged unwillingness of democracies to go to war with one another. In dozens of cases across the world, it has simply toppled democracy whenever it yielded the wrong results.

As for investing heavily, you point out yourself that offence spending is greater than ever. In fact, the USA spends more on "defence" than the next 11 countries combined. This is actually a crucial element in its continuing decline: The USA has squandered trillions of dollars and decades of time on pointless wars, while the rest of the world has invested in its people and infrastructure. America has gone in my lifetime from the world's greatest creditor nation to its greatest debtor, while its incomes have stagnated for 30 years and ordinary people are born and die in debt. Bellicosity has ruined America.

The next big war may well be between Americans.