declare war

noun

1. open armed conflict between countries or between factions within the same country
2. any active hostility, contention, or struggle; conflict: the war against disease
3. Obsolete a battle
4. military operations as a profession or science

adjective

intransitive verb warred, warring

1. to carry on war; engage in military conflict
2. to be in a state of hostility or contention; contend; strive