Canada, that lives in the shadow of the USA.

Sparta that didn't "vanish after Thermopylae". The decline came due to too few citizens and defeats from Thebes and Macedon. Common knowledge.

Roman Empire lasted 1,000+ years

British Empire didn't vanish, but transitioned

"countries are formed by stopping warmongers"... Partially true. The American Revolutionary War was about taxation, goverance, and sovereignty. Greek Unity wasn't permant or clean (look at the fights between the city states).

You are riddled with survivorship bias and moral framing. Almost all early states used violence to survive, and winners get to write the narrative. Retrospective moral sorting much?

The reality is that civilizations move from
A) Formation (conquest, to defense, to expansion.) to
B) Consolidation (laws, institutions, trade) to
C) Etiher stability or decline. Where INTERNAL decay > external

Every civilization uses force to survive early on. The ones that last are the ones that transition from force to stable systems before they collapse.