Source for the reference to the Basque name for god? Bartleby.com says it's from a british patriotic song, “We don’t want to fight, but, by jingo, if we do … .” from the 1870s.
As someone else pointed out, the OED says it's "as yet not supported by the evidence" that it's the Basque god:
—This comment was unsigned.
- I don't see the utility of removing it. Indicating that it may be disputed is one thing, but removing it is akin to simple vandalism. --Connel MacKenzie 18:16, 24 August 2006 (UTC)
Encarta is specific about the origin of jingoism in a song: The context of the coining of jingoism was British foreign policy of the late 1870s. The prime minister, Benjamin Disraeli, favored sending gunboats to halt the advance of the Russian fleet out of their own waters into the Mediterranean. This gave rise to a music-hall song, written in 1878 by G. W. Hunt, the refrain of which went: "We don't want to fight, yet by Jingo! if we do, We've got the ships, we've got the men, and got the money too." Opponents of the policy picked up on the word jingo and used it as an icon of blind patriotism.
As for jingo, www.etymonline.com says: As an asseveration, it was in colloquial use since 1694, and is apparently yet another euphemism for Jesus, influenced by conjurer's gibberish presto-jingo (1670). The suggestion that it somehow derives from Basque Jinko "god" is "not impossible," but "as yet unsupported by evidence"