Peace, Ceasefire, or Stalemate? How Wars End and the Road Ahead for Ukraine

Commentary by Benjamin Jensen and Jose M. Macias III

Published November 8, 2024

There are already outlines for a negotiating settlement to the war in Ukraine emerging from the Trump team. Yet, any negotiation strategy and approach must consider the reality of war termination and how modern interstate wars end. Surveying data on modern conflict and major studies suggests that the next administration should pivot and frame negotiations from a position of strength that guarantees military support and signals a willingness to remove restrictions on Ukrainian deep strikes. Negotiating an end to war is a coercive bargain and the Kremlin needs to understand the costs and consequences of perpetuating its unjust invasion.

First, any strategy to negotiate an end to the war in Ukraine must start with surveying data on how wars end in the twenty-first century. Based on analyzing data from the Uppsala Conflict Data Program, conflicts often don't end as much as decline to lower levels of violence. Forty percent of all wars end without a formal agreement and sixty-six percent of all wars end in some compromise ranging from a stalemate or a formal ceasefire and/or a peace agreement. Looking specifically at interstate wars, the same pattern holds. Only 30 percent of wars between states end with a victory by either side. Even when there are higher-intensity wars, such as the conflict in Ukraine, that see thousands of deaths per year, compromise and stalemates are the most common outcome with 54 percent of conflicts ending in either lower activity, a ceasefire, or a peace agreement.

What does this mean for Ukraine? Thirty-one percent of high intensity interstate wars end in a stalemate under ceasefire agreements, which halts large-scale violence but leaves underlying disputes unresolved. This trend underscores the probability of a "frozen conflict" for Ukraine, where active hostilities might subside without a formal peace, potentially stabilizing frontlines but leaving the core conflict unresolved. As a result, the Trump administration needs to ensure it makes long-term plans for providing Ukraine the means to defend itself and deter a future conflict.

Second, any strategy to accelerate the end of the war in Ukraine should factor in the findings of decades of research on war termination. This literature finds that how each state assesses the costs of conflict impacts the duration of wars and the terms of settlement. These costs include the human toll-both in death and the psychological effects of violence-alongside political risks to leaders and lost economic potential from converting resources into military power. Yet, in calculating the costs and benefits of continuing a war, information plays a central role. States must come to a tacit agreement about their military power and ability to sustain a conflict relative to the adversary and prevailing trends before they can come to the table to bargain. Cost calculations also take into consideration domestic politics and psychological factors. Expectations about post war settlements further constrain this bargaining space. And war policies become institutionalized overtime, making it difficult for leaders to negotiate. As a result, ending any war requires a change in the domestic governing coalition, with new elites injecting ideas about strategies for ending a war.

What does this mean for any proposal to negotiate an end to the war in Ukraine? First, wars aren't just about the battlefield. War weariness, domestic politics, and intelligence estimates play a critical role in shaping how each side develops a strategy for the end game.

It also implies that signaling a willingness to reduce support to Ukraine risks strengthening Russia's bargaining position and complicating negotiations. Elites around Putin need to know that Ukraine will have the international backing it needs to fight next campaign season, without restrictions, and that the Russian economy may never recover if the Kremlin doesn't sit down to negotiate. Second, future expectations shape present day strategy. Moscow and Ukraine need to be confident that both European and U.S. support for Ukraine will continue for at least a decade. That doesn't mean the United States pays the lion's share, but it does mean U.S. leadership brokers a long-term funding and reconstruction strategy that supports any negotiation.

All wars come to an end. How they end is a function of strategy that bridges military campaigns with long-term diplomatic support and negotiation tactics. The Trump administration is justified to call for plans to end the conflict but should be mindful of the record of how wars end in the twenty-first century and enter negotiations alongside Ukraine from a position of strength.

Benjamin Jensen is a senior fellow for Futures Lab in the International Security Program at the Center for Strategic and International Studies (CSIS) in Washington, D.C., and the Petersen Chair of Emerging Technology and professor of strategic studies at the Marine Corps University School of Advanced Warfighting. Jose M. Macias III is an associate data fellow in the Futures Lab within the International Security Program at the Center for Strategic and International Studies in Washington, D.C.

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