Third-party pressure for peace

Third-party pressure for peace is any threat issued or any penalty applied toward one or both sides of the warring dyad with an intention to halt hostilities. Some studies find that pressure shortens peace, while others conclude that it has no effect. This paper advances our understanding of how outside pressure affects peace by differentiating the levels of costs associated with various instances of pressure. I argue that outside pressure to halt hostilities leaves at least one belligerent in the dyad unhappy with the political settlement, because reputational or other costs force belligerents to accept settlements that do not fully reflect a potential military outcome. Disagreeing with political settlement provides incentives to revise it. More crippling types of pressure raise the cost of another war, making formal renegotiation off the battlefield more attractive even in the presence of bargaining failures. Cheaper methods of pressure do not. I test this intuition, using original data on all cases of outside pressure for peace in a sample of ceasefires initiated in 1914–2001. The results show that diplomatic pressure is associated with ceasefire breakdown, while economic pressure has no effect in the long run (most instances of economic pressure coincide with diplomatic sanctions), and military pressure is associated with longer peace. To circumvent the empirical challenge of outside actors selecting themselves into certain types of wars, I also match ceasefires, so that the most similar cases with and without pressure are compared; all results hold.