I've been involving my players in the buildup of a war, and soon they will be plunged into the thick of it.
Background: Small, low-level party in the Silver Marches region (Forgotten Realms). As the game began (last December), the players learned that an orc horde is gathering in the North, under the banner of King Obould Many-Arrows. War is coming.
1. (January) They clear out and claim a small keep in the mountains overlooking a strategic mountain pass. In the process, they learn that the Orcs have allies in a nearby Dark Moon monastery.
2. (January) Party begins the process of fortifying and arming their new keep. They forge a relationship with the nearest human community (the town of Deadsnows).
3. (February) Party investigates nearby orc tribes and discovers an envoy of King Obould has been bribing local chieftains to join the horde. The Party is able to prevent two large tribes from allying with Obould. Unfortunately (and unbeknownst to them), they fail to prevent Obould's envoy from convincing a band of Trolls from joining the war against the Marches. This mistake will come back to haunt them, as the trolls will launch an attack on the very pass that the party's keep is guarding (March).
4. (Projected: February) With renovations complete, the party will undertake a diplomatic mission on behalf of Deadsnows. They will be sent to Silverymoon in order to petition the Silver Council to admit Deadsnows as a protectorate. If they succeed, they will be able to draw upon the martial resources of the region. If they fail, then they will essentially be on their own in the coming battle.
5. (Projected: March, weeks 1 & 2) The first two weeks of March will be occupied with preparations. They will be encouraged to tie up any loose ends (the Dark Moon Monks, the local Orc tribes, the trolls, etc.) in addition to shoring up their defenses (buying weapons, arming the locals, hiring mercenaries, etc).
6. (Projected: March, week 3) War begins with attacks throughout the southern Marches---incuding Deadsnows. Unfortunately, I can't provide much more detail as everything depends on the PC's actions over the next month.
Essentially, I'm playing the war in a completely fair manner. The actions of the players will have a direct and noticeable effect on the face of the war (in their area at least). If the party is lazy or careless, the horde will have many more allies to draw upon---and the region will suffer from lack of preparation.