jingo
One who supports policy favouring war.
The fact is that Mr. Roosevelt has always with perfect frankness confessed himself to be what is currently called a Jingo.
1897 June 19, Carl Schurz, editorial: Armed or Unarmed Peace in Harper's Weekly, reprinted in 1913, Frederic Bancroft (editor), Speeches, Correspondence and Political Papers of Carl Schurz,
Where it comes from
From the minced oath by jingo, which was used in a music hall song, written ca. 1878 by G. W. Hunt, that supported Britain's then belligerent attitude towards Russia. In this context, a euphemism for Jesus, influenced by the meaningless presto-jingo used by conjurors. A connection with the Basque jainko (“god”) has been suggested, but evidence is lacking.
Adapted from the Wiktionary entry jingo (CC BY-SA 4.0).