The Second Nagorno-Karabakh War in 2020 was a major armed conflict between the two modern, regular armies of Armenia and Azerbaijan. This open access book examines the causes, and consequences of the war Second Nagorno-Karabakh War. The first part of the book includes chapters discussing why the ceasefire regime failed after long twenty-six years, international mediation and diplomacy, the geopolitical tensions, Armenia’s failure to anticipate the coming war, and emergence of autocratic rule in Azerbaijan. The second part of the book looks at international actors, including the surprising behaviour of Russia, Turkish role and interests, and the lack of American Christian solidarity towards Armenians. The third part of the book looks at the consequences of the war, including the post-war diplomatic initiatives, the dramatic failure of the Russian peacekeeping mission leading to the ethnic cleansing of Nagorno-Karabakh, and a comparative study of Nagorno-Karabakh with the Russia-Ukraine wars. Including specialists from various disciplines and from several countries, the book sheds light on the Second Karabakh War, the future of Armenian-Azerbaijani relations and placing it in the broader international context of a new era of inter-state wars. The ebook editions of this book are available open access under a CC BY-NC-ND 4.0 licence on bloomsburycollections.com.