Русско-англо-русский юридический словарь

A peace treaty is an agreement between two or more hostile parties, usually countries or governments, which formally ends a state of war between the parties. (Wikipedia)

North Korea has said it is entering a "state of war" with South Korea in the latest escalation of rhetoric against its neighbour and the US. (BBC News)

A declaration of war is a formal act by which one nation goes to war against another. The declaration is a performative speech act (or the signing of a document) by an authorized party of a national government, in order to create a state of war between two or more states. (Wikipedia)

Great Britain is in a state of war with Germany. It was officially stated at the Foreign Office last night that Great Britain declared war against Germany at 7pm. The British Ambassador in Berlin has been handed his passport. (bbc.co.uk)