go to war

/G OW1 T UW1 W AO1 R/
verb
  1. 1

    To enter into an armed conflict.

  2. 2

    (of a person) To depart, typically from one's home, to join an army at war.

    โ€œAt the age of nineteen, my grandfather went to war.โ€

Source: https://en.wiktionary.org/wiki/go%20to%20war