Garnfellow
Explorer
The Grim Tales system is really excellent -- to me it hits the perfect balance of detail and simplicity. I would use it to resolve any large-scale conflict that the PCs are not directly involved in as commanders or soldiers.
As Wulf said, the Fields of Blood system is great if war is going to be an ongoing, central focus of a long-term campaign. But if this is going to be a temporary side-show, it's probably far too much detail for your purposes.
I am also a HUGE fan of the representative battle rules from Green Ronin's Advanced Game Master's Guide. Basically, you have the PCs play through a series of small scale battles that are representative of the larger scale conflict. If the PCs win these small battles, the larger army wins the battle. Modifiers due to circumstances (larger armies, better troops, better positioning) can make the small-scale battle tougher or harder for the PCs.
So if you were going to resolve the battle of Helms Deep using these rules, rather than stat out the whole orc army and all the defenders, you would run a representative battle with just Aaragorn, Gimil, and Legolas taking on individual sorties of orc raiders.
I used this system in my last game and my players loved it. We had tried out some other systems to resolve big, in-game battles -- like Mongoose's Open Mass Combat System (OMCS). But my players weren't much interested in learning a new sub-system, and didn't like that their PCs largely got lost in the shift of scale. The Representative Battle system let them be right in the thick of the action without having to add on lots of new rules.
As Wulf said, the Fields of Blood system is great if war is going to be an ongoing, central focus of a long-term campaign. But if this is going to be a temporary side-show, it's probably far too much detail for your purposes.
I am also a HUGE fan of the representative battle rules from Green Ronin's Advanced Game Master's Guide. Basically, you have the PCs play through a series of small scale battles that are representative of the larger scale conflict. If the PCs win these small battles, the larger army wins the battle. Modifiers due to circumstances (larger armies, better troops, better positioning) can make the small-scale battle tougher or harder for the PCs.
So if you were going to resolve the battle of Helms Deep using these rules, rather than stat out the whole orc army and all the defenders, you would run a representative battle with just Aaragorn, Gimil, and Legolas taking on individual sorties of orc raiders.
I used this system in my last game and my players loved it. We had tried out some other systems to resolve big, in-game battles -- like Mongoose's Open Mass Combat System (OMCS). But my players weren't much interested in learning a new sub-system, and didn't like that their PCs largely got lost in the shift of scale. The Representative Battle system let them be right in the thick of the action without having to add on lots of new rules.