noun, noun or participle which takes 'suru', intransitive verb
outbreak of war; start of hostilities
Refers to the formal commencement of war or armed conflict. Often used in historical or news contexts. As a suru-verb, it is intransitive: 開戦する means 'war breaks out' or 'hostilities begin'.
1941年12月に日本はアメリカと開戦した。
Japan went to war with the United States in December 1941.
開戦の知らせが全国
News of the outbreak of war spread throughout the country.