Oh By Jingo

The word jingo came from the Basque word Jainko, meaning God, so the expression "by Jingo!" is the same as "by God!" Brewer's states that this term started to be used when Basque soldiers were imported by Edward I (1239-1307) to fight in Wales.

Between that time and the Russo-Turkish War (1877-78), the adjective "jingo" was used to describe a rather vulgar person (someone who would say "by Jingo"). 

Jingoism means extreme nationalism characterized by shows of excessive patriotism, usually associated with going to war. This word came about when England was considering involvement in the Russo-Turkish War. A music hall song of that time proclaimed:

"We don't want to fight: but if we do, by Jingo, 
We've got the ships, we've got the men, and got the money, too!"

Jingoism became the term for the sentiment expressed in the song and a jingoist is a person who embodies that sentiment.   From:  Jingo and Jingoism, by Jingo!

OH BY JINGO

In the land of San Domingo
Lived a girl called Oh By Jingo
(Ta da, ya da da da da da, um-pa, umpa um-pa um-pa)
From the fields and from the marshes
Came the young and old by goshes.
(Ta da, &c.)
They all spoke with a different lingo
But they all loved Oh By Jingo
And every night
They sang by the pale moon light

Oh By Gee, By Gosh, By Gum, by Jove,
Oh By Jingo, won't you hear our love!
We will build for you a hut
You will be our favorite nut.
We'll have a lot of little Oh By Gollies
Then we'll put them in the Follies.
By Jingo said, By Gosh By Gee-ee,
By Jimminy, please don't bother me.
So they all went away singing
Oh By Gee, by gosh, By Gum, By Jove, By Jingo,
Oh, By Gee, you're the only girl for me.

Oh By Jingo had a lover
He was always under cover.
(Ta da, &c.)
Every night she used to meet him.
Oh how nice she used to treat him.
(Ta da, &c.)
They eloped, but they both were collared,
And the gang stood there and hollered:
"Don't raise a fuss,
You've got to take one of us!"

Oh by Gee, by Gosh, by Gum, by Jove
Oh! By Jingo, won't you take our love?
We will live out in a tent
Cheat the landlord of his rent
We'll have lots of little Jimminy Crickets
We can use them for meal tickets!
By Jingo said, Oh boys, won't you behave
You know I've put five husbands in the grave.
So they all went away singing
Oh by Gee, by Gosh, by Gum, by Jingo,
Oh by Gee! You're the only girl for me.

Oh by Gee by Gosh by Gum by Jove
Oh By Jingo won't you hear our love?
We will build for you a still
We'll make whiskey on the hill
We'll have a lot of little liquor beggars
They'll grow up to be bootleggers!
By Jingo said now boys, don't rave
You know I've put six husbands in the grave.
So they all went away singing
Oh by Gee, by Gosh, by Gum, by Jove, by Jingo;
Oh by Gee, you're not the girl for me.

  Songs referenced: 

After All