In the age of imperialism at the height of both Darwinist and Clanker powers, strange things started happening. Airships on both sides started disappearing and the rare survivors were covered in burns and reported seeing strange crafts before blanking out.
Each nation confident in its own abilities, attempted to take out the strange crafts that were attacking their ships by themselves. Some nations met with more success than others most notable Germany who managed to take out a small craft that was rendered unsalvageable in the battle but at the loss of 3 airships.
Scared and licking their wounds, all of the major nations gathered under one roof and after much talk created an organization dedicated to stopping this threat to humanity and their ambitions. This organization was named quite unimaginatively the Institution.
The Institution was allowed practically worldwide basing rights it's newly selected leader immediately beginning franchises in the capitals of all 12 of its funding nations with its central headquarters in neutral Switzerland.
The Institution was afforded the best soldiers, scientists, fabricators, engineers and gear the funding nations could provide like the new and safer 10 Shooter Colt Revolving Rifle or the experimental Lightning Interceptor Crafts.
And so begins the war against the alien incursion.
Author's note
TL:DR
X-Com in the Leviathan universe with some changes to fit the technology
yes this can be considered a challenge I may continue if inspiration hits me.