text: War is a conflict involving use of weapons and physical force by states or other large-scale groups, coinciding with a lack of dialogue between the parties. Warring parties usually hold territory, which they can win or lose; and each has a leading person or organisation which can surrender, or collapse, thus ending the war. Wars are usually a series of military campaigns between two opposing sides involving a dispute over, amongst others issues, sovereignty, territory, resources, religion, or ideology. A war to liberate an occupied country is called a "war of liberation"; a war between internal factions within a state is a civil war. Until the end of World War II, participants usually issued formal declarations of war.\n\nOther terms for war, often used euphemistically to circumvent limitations on war, include armed conflict, hostilities, and police action. A time when no formal war is taking place, although there may be international and internal tensions, is sometimes called peacetime or peace. However, some consider the definition of peace to be more complicated. Baruch Spinoza (1632–77) said, "Peace is not an absence of war, it is a virtue, a state of mind, a disposition for benevolence, confidence, justice."\n\nWar almost always results in many unnecessary deaths. In the wars and conflicts of the 20th century, an estimated 130–142 million people died, of which 51 million occurred after the end of World War II