Ya, I did a campaign that started with the kidnapping of the king, a evil uncle taking over and then the southern providence refusing to obey him and civil war erupted.
THe first few adventures they were in the capital city. THe kidnapping happened while they were there and the city was placed under martial law as the evil unlce took over everything. There was some fighting in the streets and many people ran from the city if they could. The party, like everyone else, was really caught unaware and ended up having to owe the thieves guild a big favor for being allowed to be smuggled out of the city.
From there the party spent a few adventuires dodging the evil king's men, as they tried to warn people and towns and spread the word as fast as they could. During this time, they actually befriended a goblin tribe and saved them from being exterminated by the evil kinds men as they were fortifying their power base.
Around session 10 they finally got father then the evil king could really reach. They vistied a good duke of the sourthern providence and while he had heard from other sources, the PCs were one of the few first hand accounts he got. Skirmishes on the border happened for a year as armies were raised. During this time, the PCs snuck across the border to help people escape the evil king and guide them to saftey.
After a year since the campaign started, it was spring ands war was declared as the evil king invaded the southern province. THe PCs heard where the armirs were but avoide3d them as much they could. The dealt with spies and sabatores when they could, other times they were the spies and sabetores. They rescued some high officals the evil king was not able to kill and help them escape during this time.
After the first year of the war, the PCs were seeing the sourthern providence was not doing well. So, in a very good move they went back to the goblins they had rescued. They spent a good six months building relationships with the goblins and helping them out and eventually got the goblins to invade the evil kings land from the north. THat idea was completely the players and it never would have happened if they didn;'t choose to help out the goblins early in the campaign.
With a 2 sided war, the evil kings army was fought back some but it was still a tough war. The PCs at this point choose to sneak into the capital were the campaign started. They jioned the thieves guild and organized them into a strike force to attack the city from inside and spy and sabatage everything they could. The thieves guild did okay, but were soon routed by the mages the evil king had. The PCs in a very bold move, attacked the mages in the kings castle and really hurt the kings power base as the mages were responsible for scrying, communications and import things like that.
THe PCs regrouped for a day and then figured it was their best bet to go after the evil king and rescue the rightful king which they were able to do.
So, as the war was the backdrop the PCs didn't participate in any huge battles. They played smart and choose their oppurtunities and missions. They never officially worked with the sourthern duke and actually chased some spies they didn';t know where secret agents of the south for a little bit.