[jjk166]

Fear of invasion creates massive military spending

Massive military spending creates peaceful times

Peaceful times create low military spending

Low military spending creates fear of invasion

Also the Canadians are the only ones who ever burned down DC.

[aylmao]

It doesn't always work this way, and very much hasn't in the USA. It's been more akin to:

Fear of invasion creates massive military spending

Massive military spending creates a need for justification, and ability to invade

The need for justification, and ability to invade create wars abroad

Wars abroad create enemies and fear of invasion

[jjk166]

Has there ever been a period in history where the dominant military power said "okay, no one can challenge us, let's roll back our military spending" and the peace remained?

I can think of a lot of previous hegemons who got complacent and lost everything.

[aylmao]

I can't think of a period in history where most nations were democracies either, where most women could vote, or where most people had access to public education.

But alas, here we are.

[jjk166]

And I can't think of a period in history where I can use a tiny device in my pocket to order a coat with same day delivery, but somehow invading Russia in winter still seems like a bad idea.

I see no reason to believe that democracies with women's suffrage and public education are immune to military competition. I certainly wouldn't want to risk massive upheaval of the world order which jeopardizes the existence of all those things to find out.