The Second World War on the territory of the former Yugoslavia was marked by extraordinary complexity and basest brutality. At least twelve factions fought against and worked with each other in what was at the same time a liberation war, a civil war, and a revolutionary war. The human cost was staggering: out of the pre-war population of roughly 15 million, more than one million died as a direct result of the conflict. "Sea of Blood: Yugoslavia 1941-1945. Military History of Partisan Movement" (hereinafter: "Sea of Blood" will provide a military-historical take on these events. A special accent will be placed on the operational aspect of the war, but other related facets will be covered as well (e.g. the influence of political considerations on operations in the field, the question of war crimes and reprisals, etc.). The narrative will follow the creation and rise of the communist-led People's Liberation Movement and more specifically its combat arm, colloquially known as the Partisans. The "Sea of Blood" will also deal heavily with Axis counterinsurgency efforts, particularly those carried out by armed formations of the Third Reich. Although the past decade has seen a steady rise in the number of academic publications in English dealing with various military aspects of the war, none of them offers a comprehensive coverage of the entire conflict. The main deficiency of most scholarly works from outside of what was once Yugoslavia is the over-reliance on Axis/non-Yugoslav primary sources; the "Sea of Blood" will seek to redress the imbalance by drawing heavily on both original Yugoslav documents and a vast array of secondary sources published in the region over the past 70 years. The manuscript will also cite unpublished materials from more than a dozen archival institutions including NARA, TNA, TsAMO, BA/MA, Military Archives in Belgrade, and national archives from practically every former Yugoslav republic. The "Sea of Blood" will find readership among all those interested in the Second World War in Yugoslavia, history of guerrilla warfare, and contemporary history of the Western Balkans. The main narrative is divided into seven chapters. Additional information is provided in the introduction (which comes together with a bibliographical survey) and three appendices, which contain a short treatise on human losses, as well as tables and organizational charts; the text is accompanied by a dozen maps.