I have an idea for an unusual campaign with Lawful Evil Hobgoblin PCs.
The Hobgoblins are lead by a Chancellor-General in a strict military society, something like Germany under Otto von Bismark. There are laws, and there's no slavery, but it's proto-fascist.
Spies have said that the neighboring lawful-good human empire (something powerful, baroque, pious, decadent, and corrupt like France under the Bourbons) is readying for an attack. All military age hobgoblins are called to the front lines.
The attack comes. The war goes poorly and the humans overrun a portion of the hobgoblin nation. Now a band of teenage hobgoblins just too young for military service are hiding outside of their hometown where a company of human soldiers has occupied, led by at least one paladin.
So it's Red Dawn with Hobgoblins. The action is taking place in a war zone. A governing occupation of clerics and paladins has taken over the urban centers, but there's a scattered and disorganized resistance with fragile lines of communication and supply.
I've got the big idea down, but I need ideas for specific adventures and encounters. I'm starting the party at 1st level. I see early adventures being gathering supplies, creating a network by helping out farmers and others, and picking off isolated squads of human troops. The humans will have celestial animals and trained monsters on their side. The normal military presence defending the roads and small villages from monsters is gone. The hills around town contain a few old forts and catacombs where some equipment was stockpiled, but are now overrun with squatters of one species or another.
I want to alternate between short traditional dungeons and wilderness encounters, underground resistance social encounters, and tactical combat with soldiers. There's going to be a lot of enemies with PC levels.
Wide open to ideas.
Stealth seems like a good idea. Poison the food they have, destroy carts or sabotage wheels, anything that makes it so the humans are either confused, scared of hobgoblin 'ghosts' or planning to leave.
Check out James Jacob's and Keith Baker's old 3.5 adventure Red Hand of Doom. While that was focused around humans trying to stop an advancing army of hobgoblins, there's a lot of good material there that you could adapt. Also the 3.5 book Heroes of Battle is a good resource for wartime adventures.