There are more than a dozen chapters in the Scenario mode. Here you engage in epic PVE battles by doing the main quests.

In each chapter, you need to occupy all ten fortresses in order to unlock the next map.
There will be new generals waiting in some of the fortresses. You need to defeat them first or complete relative quests in order to recruit them.
Defeat to recruit

Resource Scenario

Sometimes carts carrying resources or EXP will appear along the road. By defeating some of the NPCs, you can challenge those resource scenarios free of charge (within a time limit).

You can challenge them again at any time for a cost.

Resources scenario
Also there will be bonus scenario if you defeat certain NPCs.