Here is an example of how seasons can influence campaings:

Phase 1 is Spring. The Campaign map is hidden by fog of war. You are dropped (typically naked) into an unknown, deadly environment. This world is filled with the ruins of ancient castles, abandoned mines and haunted villages – which you have to explore to scavenge for weapons, tools and the resources to start building fortifications.

Phase 2 is Summer. The Hunger starts to infect the creatures. Resources become scarce. Your team claims an abandoned quarry and must fight to keep it. You use the stone to build an ancient keep, to use it as a staging area to attack your neighbors.

Phase 3 is Fall. The creatures become more deadly as the Hunger takes hold. Resources are heavily contested and transporting them is fraught with peril. Your guild frantically builds a wall around your city, as the nature of conflict shifts from smaller skirmishes to siege warfare.

Phase 4 is Winter. The environment is brutal. Warmth is hard to come by. Your kingdom grows in strength; your neighbors falter and you demand that they swear fealty or face complete loss of the Campaign. Instead, a handful of smaller kingdoms choose to band together against you.

Phase 5 is Victory and Defeat. The World is destroyed in a cataclysmic event as the Campaign comes to an end. Your Kingdom emerges victorious, and you return to the Eternal Kingdoms to enjoy the spoils of war. Your adversaries head home, too -- to lick their wounds.