How could the variations in the level of peace, order, institutionalization and cooperation in the various regions in the twenty-first century be explained? The author argues that the combined effect of two factors—state capacity and national congruence—is the most important, although an additional factor can mitigate or aggravate their effects—great power intervention. The two key factors are state capacity—the effectiveness of the functioning of state institutions; and national congruence—the extent of congruence between geo-political boundaries and national aspirations and identities in the region (including notably issues of national self-determination). Regions in which the states are strong and nationally coherent will tend to produce warm peace (Europe and South America). Regions in which at least some of the states are failed states—both weak and incongruent—will generate hot civil wars and trans-border violence (Africa, South Asia and the Middle East); while regions with strong states but incongruent will tend to produce a revisionist model and cold wars among strong states (East Asia and the post-Soviet). Finally, the instability prevalent in regions populated by failed states can sometimes be mitigated by the intervention of a benign hegemon and produce cold peace (the Balkans in the 1990s), but in highly fragmented regions such interventions might face a lot of problems and have some de-stabilizing effects, producing domestic and regional violence (South Asia and the Middle East).