External threats help, but unification was often, ahem, self-promoting as well. A hundred years on, becoming Roman by force and becoming Roman to avoid becoming Persian was kind of indistinguishable - and both did happen.
We’re kind of in uncharted territory with today’s ideologically-driven democracies, but I’d argue the EU itself is a kind of peaceful equivalent. New members accrue because the economic and other benefits vastly exceed whatever beef it’s neighbors have with it.
External threats help, but unification was often, ahem, self-promoting as well. A hundred years on, becoming Roman by force and becoming Roman to avoid becoming Persian was kind of indistinguishable - and both did happen.
We’re kind of in uncharted territory with today’s ideologically-driven democracies, but I’d argue the EU itself is a kind of peaceful equivalent. New members accrue because the economic and other benefits vastly exceed whatever beef it’s neighbors have with it.