Whenever I start a new campaign in a setting I've already used, I usually set it years after my previous campaign, which provides some of the backdrop for the present. In my current Wandering Heroes of Ogre Gate campaign, I am using the final events our last adventures to establish the current set-up. Something significant was coming to a head in our prior campaign and the fallout from that conflict had a huge impact on the martial world: The Battle of Je Valley. The players in the new campaign will be exploring an environment shaped by those events, with lingering grudges and hostilities in the air. However because the new session will take place ten years later, most of the characters were just children when the last campaign ended.
This is somewhat inspired by the Condor Heroes Trilogy, where the heroes of the first book essentially become major NPCs in the second book, and the new protagonist is the child of one of the old villains. What I find this does is it creates a fertile environment for adventure and conflict. There is no pre-planned campaign arch or story. This is more about having a set of interesting pieces on the table, with ties to some of the players, to give a sense of rootedness.
In my current game, the players will not be fighting the same battles or seeking the same goals as the last one, but the past will reverberate and persevere into the present. The resilient characters who survived the Battle of Je Valley, remain active participants in the politics of the martial world. Some still nurse grudges and are even more steadfast in their desire for justice. In essence, the survivors of Je Valley are the elders of the new campaign.