Ferguson’s Law

"What I call Ferguson’s Law states that any great power that spends more
on debt service than on defense risks ceasing to be a great power. The
insight is not mine but originates with the Scottish political theorist
Adam Ferguson, whose “Essay on the History of Civil Society” (1767)
brilliantly identified the perils of excessive public debt.
..
Economists have long sought in vain a threshold that defines how much
debt is too much. My own formulation of Adam Ferguson’s idea focuses our
attention on the crucial historical relationship between debt service
(interest plus the repayment of principal) and national security
(expenditure on defense, including investment in research and
development).
The crucial threshold is the point where debt service exceeds defense
spending, after which the centripetal forces of the aggregate debt
burden tend to pull apart the geopolitical grip of a great power,
leaving it vulnerable to military challenge.
The striking thing is that, for the first time in nearly a century, the
U.S. began violating Ferguson’s Law last year. Annual defense
spending—to be precise, national defense consumption expenditures and
gross investment—was $1.107 trillion in 2024, according to the Bureau of
Economic Analysis (BEA), while federal expenditure on interest payments
(the government long ago gave up on paying down principal) topped out at
$1.124 trillion.
..
Ferguson’s Law—that it is dangerous for a great power to spend more on
debt service than on defense—is borne out by history."
The author uses the rest of the article to related Ferguson's law with
the decline of the Spanish, the French, the Ottoman Empire, and the
British Empire.
https://www.wsj.com/politics/policy/debt-has-always-been-the-ruinof-great-powers-is-the-u-s-next-02f16402?