Third person
The two campaigns would be:
Campaign 1: Cortez
Be in a conquistador army alongside cortez during the conquest of Mexico fighting the mayans. But, something strange is afoot. As the conquest continues, the mayans seem to dissapear. You come across several abandoned villages and towns, and as you travel further northward, you discover why. A strange race of ungodly alien eldritch abominations are invading North America. They propagate themselves through the universe by devouring all life on planets and covering them in their biomass, fresh to produce more of them. They have already completely covered North America, and are headed towards mexico and russia. You discover some of their artifacts made of a strange blue glowing metal, shortly before leaving back to the old world to tell the news.
Campaign 2: Napoleon
I wont go into much detail but it would go something like some alchemists discover how to replicate the blue metal and it turns out they have magic properties, and napoleon uses this to reign across the globe. The campaign would be fighting the wars using magic tools
Then there would be a sequel
Campaign 1 would be taking down napoleons empire, campaign 2 would be fighting the eldritch abominations.