Russo-Ukrainian War: 2014–???? Why did it start? Why does it continue? How may it end?

The Russo-Ukrainian War began in 2014 and expanded into a full-scale invasion in February 2022. This article explains both transitions, the continuation of combat despite immense costs to Russia and Ukraine, and the war's most likely outcome. It reconstructs the conflict from the divided historical inheritance of Kievan Rus through post-Soviet disputes, NATO enlargement, Euromaidan, Crimea, Donbas, the Minsk process, and the 2021 crisis. The analysis gives greater evidentiary weight to theories of causation that produced specific warnings before the outcome. George Kennan, William Burns, and John Mearsheimer warned that Ukraine's westward military alignment could produce violent confrontation; Mearsheimer specifically predicted that continued efforts to make Ukraine a Western stronghold would lead Russia to 'wreck' the country. On this basis, the article identifies NATO enlargement, Russia's exclusion from decision-making authority in the Euro-Atlantic security system, and Ukraine's increasing military alignment with Western states as the principal cause of the conflict. This conclusion explains conduct; it does not justify Russia's decision to use force. Imperial-nationalist, regimesecurity, economic, and personalist explanations clarify some Russian objectives, assumptions, and operational errors, but most did not distinguish a full-scale invasion from continued coercion before Russian preparations made an attack imminent. The article therefore criticizes multi-factor theories that can explain everything and predict nothing. It also examines the danger described as a 'Cuban Missile Crisis in reverse.' A strike system deployed in northern or eastern Ukraine could leave Moscow only minutes to detect and classify a launch, communicate the warning, and decide on a response. Interception cannot be guaranteed: ballistic speed reduces the engagement window, while a maneuvering hypersonic weapon may be detected late and may change course, making timely interception impossible in a particular engagement. This warning-time problem became more consequential as arms-control restraints weakened. The United States withdrew from the Anti-Ballistic Missile Treaty in 2002 and from the Intermediate-Range Nuclear Forces Treaty in 2019; Russia suspended implementation of New START in 2023; and New START expired in February 2026 without a successor agreement. These developments do not show that NATO had deployed nuclear missiles in Ukraine, and they do not legalize the invasion, but they help explain Russian assessments of future military risk. Russia's attempted rapid settlement by force failed, and the war became attritional. Western support enabled Ukraine to continue resisting, while Russia's larger mobilization base and external support enabled it to absorb losses. A decisive victory by either side and an immediate comprehensive peace treaty remain improbable. The most likely outcome is an armistice comparable in institutional form, but not in historical detail, to Korea: large-scale combat stops along a fortified line of control, territorial and legal claims remain unresolved, both sides retain substantial forces, and outside powers continue security and economic support. This is a conditional forecast, not a policy preference.