The article explores the causes and consequences of the 2020–2023 Karabakh War between Armenia and Azerbaijan. Azerbaijan reclaimed large parts of territories within 44 days of the war in 2020, the country lost control in the early 1990s and was only hindered from full control by a Russian-brokered ceasefire. Over the subsequent three years, Azerbaijan gradually asserted dominance, reclaiming all lost territories by 2023. The study probes the war’s causes and Azerbaijan’s military success. It focuses on power imbalances and strategic dynamics between the two countries that led to the war. By applying the offence–defence theory, it argues that shifting economic and military strengths rendered war inevitable due to deadlock in negotiations. Azerbaijan’s military investment, modernisation and purchase of advanced technological armament changed the balance between the two states and increased its offensive advantage. The article also examines underlying regional power competition, shaping post-war dynamics in the South Caucasus.