by jin a go go
https://en.wikipedia.org/wiki/Jingoism
The chorus of a song by the songwriter G. W. Hunt, popularized by the singer G. H. MacDermott – which was commonly sung in British pubs and music halls around the time of the Russo-Turkish War of 1877–78 – gave birth to the term. The lyrics included this chorus:

We don't want to fight but by Jingo if we do
We've got the ships, we've got the men, we've got the money too
We've fought the Bear before, and while we're Britons true
The Russians shall not have Constantinople!

The phrase "by Jingo" was a minced oath, scarcely documented in writing, used in place of "by Jesus".