Civilian in the context of "Open city"

World War II was the deadliest military conflict in history. An estimated total of 70–85 million deaths were caused by the conflict, representing about 3% of the estimated global population of 2.3 billion in 1940. Deaths directly caused by the war (including military and civilian fatalities) are estimated at 50–56 million, with an additional estimated 19–28 million deaths from war-related disease and famine. Civilian deaths totaled 50–55 million. Military deaths from all causes totaled 21–25 million, including deaths in captivity of about 5 million prisoners of war. More than half of the total number of casualties are accounted for by the dead of the Republic of China and of the Soviet Union. The following tables give a detailed country-by-country count of human losses.

Recent historical scholarship has shed new light on the topic of Second World War casualties. Research in Russia since the collapse of the Soviet Union has caused a revision of estimates of Soviet World War II fatalities. According to Russian government figures, USSR losses within postwar borders now stand at 26.6 million, including 8 to 9 million due to famine and disease. In August 2009 the Polish Institute of National Remembrance (IPN) researchers estimated Poland's dead at between 5.6 and 5.8 million. Historian Rüdiger Overmans of the Military History Research Office (Germany) published a study in 2000 estimating the German military dead and missing at 5.3 million, including 900,000 men conscripted from outside of Germany's 1937 borders, in Austria, and in east-central Europe. The Red Army claimed responsibility for the majority of Wehrmacht casualties during World War II. The People's Republic of China puts its war dead at 20 million, while the Japanese government puts its casualties due to the war at 3.1 million. An estimated 7–10 million people died in the Dutch, British, French and US colonies in South and Southeast Asia, mostly from war-related famine.

A war crime is a violation of the laws of war that gives rise to individual criminal responsibility for actions by combatants in action, such as intentionally killing civilians or intentionally killing prisoners of war, torture, taking hostages, unnecessarily destroying civilian property, deception by perfidy, wartime sexual violence, pillaging, and for any individual that is part of the command structure who orders any attempt to committing mass killings (including genocide or ethnic cleansing), the granting of no quarter despite surrender, the conscription of children in the military, and flouting the legal distinctions of proportionality and military necessity.

The formal concept of war crimes emerged from countries fighting and the codification of the customary international law that applied to warfare between sovereign states, such as the Lieber Code (1863) of the Union Army in the American Civil War and the Hague Conventions of 1899 and 1907 for international war. In the aftermath of World War II, the war-crime trials of the leaders of the Axis powers established the Nuremberg principles, such as that international criminal law defines what is a war crime. In 1899, the Geneva Conventions legally defined new war crimes and established that states could exercise universal jurisdiction over war criminals. In the late 20th century and early 21st century, international courts extrapolated and defined additional categories of war crimes applicable to a civil war.

The Arab Socialist Ba'ath Party – Syria Region (Arabic: حزب البعث العربي الاشتراكي – قطر سوريا Ḥizb al-Ba'th al-'Arabī al-Ishtirākī – Quṭr Sūriyā), officially the Syrian Regional Branch (Arabic: الفرع القطري السوري), was a neo-Ba'athist organisation founded on 7 April 1947 by Michel Aflaq, Salah al-Din al-Bitar and followers of Zaki al-Arsuzi. The party ruled Syria from the 1963 coup d'état, which brought the Ba'athists to power, until 8 December 2024, when Bashar al-Assad fled Damascus in the face of a rebel offensive during the Syrian civil war. It was formally disbanded in January 2025.

The party was founded on 7 April 1947 as the Arab Ba'ath Party through the merger of the Arab Ba'ath Movement led by Michel ʿAflaq and Salah al-Din al-Bitar and the Arab Ba'ath, led by Zaki al-Arsuzi. The party espoused Ba'athism, an ideology mixing Arab nationalist, pan-Arab, Arab socialist, and anti-imperialist interests. Ba'athism calls for the unification of the Arab world into a single state. It quickly established branches in other Arab countries, although it would only hold power in Syria and in Iraq. Following their ascent to power in 1963, neo-Ba'athist officers proceeded to stamp out the traditional civilian elites in order to construct a military dictatorship operating on totalitarianlines; wherein all state agencies, party organisations, public institutions, civil entities, media and health infrastructure were tightly dominated by the military establishment and the Mukhabarat (intelligence services).

Crimes against humanity are certain crimes committed as part of a large-scale attack against civilians. Unlike war crimes, crimes against humanity can be committed during both peace and war and against a state's own nationals as well as foreign nationals. Together with war crimes, genocide, and the crime of aggression, crimes against humanity are one of the core crimes of international criminal law and, like other crimes against international law, have no temporal or jurisdictional limitations on prosecution (where universal jurisdiction is recognized).

The first prosecution for crimes against humanity took place during the Nuremberg trials and Subsequent Nuremberg trials against defeated leaders of Nazi Germany and collaborators. Crimes against humanity have been prosecuted by other international courts (such as the International Criminal Tribunal for the former Yugoslavia, the International Criminal Tribunal for Rwanda, the Special Court for Sierra Leone, the Extraordinary Chambers in the Courts of Cambodia, and the International Criminal Court) as well as by domestic courts. The law of crimes against humanity has primarily been developed as a result of the evolution of customary international law. Crimes against humanity are not codified in an international convention, so an international effort to establish such a treaty, led by the Crimes Against Humanity Initiative, has been underway since 2008.

A neutral country is a sovereign state that is neutral towards belligerents in a specific war or holds itself as permanently neutral in all future conflicts (including avoiding entering into military alliances such as NATO, CSTO or the SCO). As a type of non-combatant status, nationals of neutral countries enjoy protection under the law of war from belligerent actions to a greater extent than other non-combatants such as enemy civilians and prisoners of war. Different countries interpret their neutrality differently: some, such as Costa Rica have demilitarized, while Switzerland holds to "armed neutrality", to deter aggression with a sizeable military, while barring itself from foreign deployment.

Not all neutral countries avoid any foreign deployment or alliances, as Austria and Ireland have active UN peacekeeping forces and a political alliance within the European Union. Sweden's traditional policy was not to participate in military alliances, with the intention of staying neutral in the case of war. Immediately before World War II, the Nordic countries stated their neutrality, but Sweden changed its position to that of non-belligerent at the start of the Winter War. Sweden would uphold its policy of neutrality until the 2022 Russian invasion of Ukraine. During the Cold War, former Yugoslavia claimed military and ideological neutrality from both the Western and Eastern Bloc, becoming a co-founder of the Non-Aligned Movement.

The Geneva Conventions is a term used to collectively refer to the four Geneva Conventions of 1949 along with their two optional protocols (Additional Protocols I and II), which form the core of international humanitarian law and establish international legal standards for the treatment of non-combatants in war. Negotiated in the aftermath of the World War II, the Geneva Conventions of 1949 consist of four agreements, which replaced three earlier humanitarian conventions of 1906 and 1929 and added two new conventions. The First Geneva Convention addresses the treatment of sick and wounded field soldiers, Second Geneva Convention addresses the treatment of sick and wounded sailors, Third Geneva Convention addresses the treatment of prisoners or war, and Fourth Geneva Convention addresses the treatment of civilians during armed conflict.

Aside from the UN Charter, the Geneva Conventions are among the most widely ratified international agreements. The 1949 conventions were ratified, in their entirety or with reservations, by 196 countries. Much of the international humanitarian law contained in the Geneva Conventions has become customary international law, and therefore would apply to all states and non-state armed groups, even those that are not a party to the Geneva Conventions. The legal obligations created under the Geneva Conventions are somewhat different from other international treaties in that a breach of the Geneva Conventions by one party does not furnish a directly affected party with the option to cease complying with its treaty obligations.

An order of merit is an honorific order that is conferred by a state, government, royal family, or other sovereign entity to an individual in recognition of military or civil merit. The historical background of the modern honours system of orders of merit may be traced to the emergence of chivalric orders during the Middle Ages.

Orders of merit may be bestowed as official awards by states, or as dynastic orders by royal families. In the case of modern republics, an order of merit may constitute the highest award conferred by the state authority.

Guerrilla warfare is a type of unconventional warfare in which small groups of irregular military, such as rebels, partisans, paramilitary personnel or armed civilians, which may include children in the military, use ambushes, sabotage, terrorism, raids, petty warfare or hit-and-run tactics in a rebellion, in a violent conflict, in a war or in a civil war to fight against regular military, police or rival insurgent forces.

Although the term "guerrilla warfare" was coined in the context of the Peninsular War in the 19th century, the tactical methods of guerrilla warfare have long been in use. In the 6th century BC, Sun Tzu proposed the use of guerrilla-style tactics in The Art of War. The 3rd century BC Roman general Quintus Fabius Maximus Verrucosus is also credited with inventing many of the tactics of guerrilla warfare through what is today called the Fabian strategy, and in China Peng Yue is also often regarded as the inventor of guerrilla warfare. Guerrilla warfare has been used by various factions throughout history and is particularly associated with revolutionary movements and popular resistance against invading or occupying armies.