Civilization V: The Swedish Saga, part 3 (1702 A.D. to 1868 A.D.)
The Celts prove their mettle
1838 A.D.: The peak of the Swedish Industrial Revolution sees the advent of many new technologies.
Industrialization lets me build gatling guns and see coal deposits on the map, which are needed for many Industrial-era units and buildings. I'm now researching Electricity, which will lead into Radio and bring me into the Modern Era.
The first Swedish troops equipped with repeating firearms are dispatched to Kaupang.
1840 A.D.: The Roman-Russian War begins far to the East. Meanwhile, foreign spies steal Rifling tech from Stockholm.
On the long list of my spy network's failures, this is the greatest so far. I've officially lost my infantry tech edge, which is my single greatest military advantage at this point. The one saving grace is that my unique Caroleans will win any 1-to-1 engagement with vanilla Riflemen, and I'm not aware of any other civ in this game that gets a unique Rifleman replacement.
In a counter-attack, the Danes capture Salzburg from the Celts.
Summer, 1842 A.D.: Celtic forces cross the Bay of Storms to aid Swedish invasion massing on the Northern Danish border. Its southern forces lose a skirmish with Danish knights near Salzburg and fall back behind Swedish lines.
The Danes out-tech the Celts almost as much as I out-tech the Danes, so my allies are just getting shredded here. On the bright side, they are weakening the Danes with every battle, and I'm not having to risk my units as much. In the long run, the outcome of this war is foregone unless Greece gets involved.