From Longman Dictionary of Contemporary Englishdeclare war (on somebody/something)declare war (on somebody/something)a) WARto state officially that you are at war with another country b) informalWAR to say that something is wrong and that you will do everything you can to stop it Angry residents have declared war on the owners of the factory. → declare
Examples from the Corpus
declare war (on somebody/something)• There was little the Phoenix King could do but finally declare war against one of his own realms.• When the Bush administration declared war on drugs, it had no idea what worked.• In 1686 they declared war on him in order to establish a separate company state from which they could trade.• Homosexuals, they claim, have declared war on nature, and nature has exacted an awful retribution.• Embassy, demanding they declare war on the Third World.• They have all but declared war on three government initiatives planned in and around the town.• On questions of foreign policy, only Congress can declare war or appropriate the money necessary to fight it. 