Why did the war in Ukraine start?

1. The immediate trigger: a 2022 invasion after months of military buildup

Russian forces invaded Ukraine on 24 February 2022 after a prolonged buildup of troops and equipment along Ukraine’s borders and in Belarus, and after Moscow recognised and pushed into the two separatist breakaway regions in Donetsk and Luhansk—moves announced publicly just days before the invasion ^{[4] [3]}. Western intelligence and analysts had warned of an imminent attack in early 2022 as exercises and troop movements escalated, and the Kremlin characterised the operation as a security measure and a mission to “protect” Russian-speaking regions and to prevent NATO expansion—framing that Moscow used to justify the intervention ^{[5] [4]}.

2. The 2014 rupture: Revolution, Crimea and the Donbas war as the long fuse

The root of the crisis sits in the Revolution of Dignity (Euromaidan) in 2013–14, which toppled a pro‑Russian Ukrainian president and led to Russia’s covert seizure and later annexation of Crimea in February–March 2014, followed by the emergence of Russia-backed separatist republics in Donetsk and Luhansk and an eight‑year conflict in eastern Ukraine ^{[1] [2] [3]}. That period transformed bilateral relations: what had been a mix of disputed politics and influence became an open security confrontation involving irregular forces, proxy support and repeated ceasefire failures ^{[6] [7]}.

3. Competing security narratives: NATO, geopolitics and Kremlin doctrine

A central explanation for Moscow’s decision to go to war lies in its long-standing objection to NATO’s eastward drift and to Ukraine’s growing Western orientation; Russian leaders framed Kyiv’s trajectory as an existential threat to their strategic buffer and domestic political order, arguments amplified in official essays and speeches before 2022 ^{[8] [5]}. Western policymakers and many analysts dispute that NATO posed an immediate military threat to Russia inside Ukraine, instead emphasising Ukraine’s sovereign right to seek security guarantees; proponents of the NATO-responsibility thesis argue Western policy shared blame for encouraging Ukraine’s Euro-Atlantic aspirations ^[8].

4. Local dynamics and agency inside Ukraine

Ukrainian domestic politics and nationalism—particularly after 2014—shaped the conflict as much as external pressures; Kyiv pursued reforms and closer ties with Europe, while many Ukrainians resisted Russian political influence, creating a strong national will that later proved decisive in mobilising against the 2022 invasion ^{[6] [5]}. The Donbas conflict itself produced hardened identities and grievances that Moscow exploited and that complicated peacemaking even when mediators negotiated ceasefires like Minsk ^{[1] [6]}.

5. Multiple causes, contested interpretations, and limits of the record

The causes of the war are therefore multi-layered—immediate military decisions, a decade of contested sovereignty after 2014, Kremlin security doctrines, NATO expansion debates, and Ukrainian domestic change—all interacting to produce escalation ^{[3] [2] [8]}. Sources differ on weight: some scholars and officials place primary responsibility on Russian imperialism and aggressive revisionism, while others—exemplified in the CIRSD analysis—stress Western policy and NATO as central drivers; both perspectives are documented in the reporting ^{[2] [8]}. Reporting and timelines establish the sequence of events clearly, but unraveling the subjective motives of leaders and the counterfactuals about what different diplomatic choices might have prevented goes beyond publicly available documentary proof and remains debated ^{[4] [8]}.