The world came closest to nuclear war during the Cuban Missile Crisis. We find that there existed two paths by which nuclear war might have occurred. The first path involves unrestrained hard-liners. Nuclear weapons did not deter some actors from proposing escalatory actions, including the use of nuclear weapons. Luckily, both Kennedy and Khrushchev reined in their respective hard-liners. Along the second path, situations – not known at the time – could have led to an initial use of nuclear weapons, after which events might have spiraled out of control. The US, for example, did not know that the Soviets had placed tactical nuclear weapons in Cuba. If the US had tried to invade Cuba to topple Castro – as some people advocated – then the Soviets might have used the weapons. Ultimately, Kennedy successfully used a quarantine and threatened force to compel the Soviets to withdraw their missiles from Cuba. The threat of nuclear war lingered behind these actions. In the end, however, the crisis ended not because of nuclear deterrence but rather because both sides reached a mutually acceptable bargain. Kennedy promised not to invade Cuba and to remove US missiles from Turkey; Khrushchev, meanwhile, agreed to remove Soviet missiles from Cuba.

This chapter summarizes the main lessons for diplomacy that we derive from our study. These eight lessons are: 1. A major factor separates the crises that escalate to war from those that do not; in the latter, a strong leader reins in any hard-liners who advocate going to war. 2. Individuals make a difference. 3. Contingency plays a more important role than system structure in determining whether or not a crisis escalates to war. 4. Someone must stand for peace. 5. The secret to preventing war structurally is to find a functional equivalent to war. 6. Norms and rules are important for avoiding war – and, therefore, maintaining peace. 7. War can be avoided; it is not inevitable. 8. The realist concepts of the national interest and balance of power do not always accurately describe the behavior of states.

In the Bosnian Crisis, coercion worked – both to get a state what it wanted and to prevent war. The crisis centers on a dispute between Austria–Hungary and Russia over a deal that concerns Bosnia. When things went awry and the threat of war arose, Germany presented the tsar with an ultimatum. Because Russia was still too weak after its defeat in the Russo-Japanese War, the tsar necessarily relented. He vowed privately, however, that he would never be humiliated in the face of a threat again; next time, he would not back down. Six years later (in 1914), he lived up to his vow. In accordance with the realist approach to international relations, this case shows that actors can successfully use coercion to address territorial disagreements (e.g., bring about territorial change) without that coercion leading to a war.

The Russo-Japanese War features a failure of rational bargaining theory. Indeed, it shows how difficult it is for actors to successfully reach a mutually acceptable bargain, even when many of the conditions are favorable. An obvious quid pro quo existed during the crisis, and at one point the Russian ambassador, Rosen, and the Japanese representative actually agreed to it. Nevertheless, Alekseiev, the viceroy of the Russian Far East province – and later, the tsar himself – overruled Rosen. Although we identify several factors that contributed to this bargaining failure, domestic politics played a major role. Agreement occurred at a low(er) bureaucratic level; hard-liners in Russia, however, occupied the highest decision-making level(s) and overruled the obvious solution, thereby causing an unnecessary war. It is also worth noting that when Japan decided on war, it executed a surprise attack on Port Arthur. Because this attack succeeded, Japanese decision-makers learned it was effective and repeated the strategy in 1941 at Pearl Harbor.