We present a unified theory and test of extended immediate deterrence—unified in the sense that we employ our theoretical deterrence model as our statistical model in the empirical analysis. The theoretical model is a straightforward formalization of the deterrence logic in Huth (1988) and Huth and Russett (1984), coupled with private information concerning utilities. Our statistical analysis suggests that the attacker and defender's decisions are influenced by the balance of forces, nuclear weapons, defender-protege military alliances, arms transfers, and trade, as well as the regime types of those involved. Many of these findings contradict previous research by Huth (1988) and Huth and Russett (1988). We find that many of the variables involved in the deterrence calculus are nonmonotonically linked to the probability of deterrence success or war. We illustrate the results with case studies of the Soviet-Japanese dispute over Manchukuo (1937–1938) and the Berlin Blockade (1948).