[Question] World superpowers, particularly the United States, still maintain large conventional militaries despite nuclear deterrence. Why?

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Most people agree that the United States spends far too much money on its military. Spending more than the next ten countries combined is obviously overkill. But what truly baffles me about the United States’ military spending is how much of it goes to conventional military.

Conventional military is entirely useless except for proxy wars and small-scale meddling in non-nuclear states’ affairs (e.g. the Vietnam or Afghanistan wars). If the US or another state were to use their conventional military to attack a nuclear state, they would be subject to the threat of nuclear retaliation; i.e. mutually assured destruction applies not only to nuclear aggression, but also to conventional aggression.

Of course, an attacking power might decide to call the defender’s bluff by taking only a small amount of territory, but this is very risky and a line must be drawn somewhere to avoid escalation. In the Cold War, we saw this line drawn inbetween proxy wars and direct attacks on enemy territory. If anything, the threshold has become even lower since then; Russia has directly threatened nuclear retaliation against the US if it were to send troops to Ukraine, and the US military remains largely useless.

The usual explanation for why the US wastes so much on its military is that the incentives of defense contractors, the Department of Defense, and Congress are all aligned to increase military spending, even to the detriment of the citizens. This makes sense for military spending in general, but I don’t see why they would spend so much on conventional military; why not just spend it on nuclear weapons and defense research?