Democratic Peace Theory
The empirical finding, with philosophical roots in Kant's 1795 'Perpetual Peace,' that consolidated democracies have almost never gone to war with one another — narrower than the popular claim that democracies are peaceful in general. Faces serious critique on definitional grounds (how 'consolidated democracy' and 'war' get classified), small-N fragility, and Sebastian Rosato's challenge to its proposed causal mechanisms. Russia's 2022 invasion does not formally counter the theory, since Russia is not classified as a consolidated democracy, but that fact alone does not settle whether the theory's underlying logic holds up well.