Magic is the lifeforce of all living creatures, and it is from it that all life is made - in areas with lots of undead, magic might actually be missing or weak, which puts a whole new spin on how dangerous the undead are. Even simple zombies can be troublesome if you're relying on mages and you hit a pocket of undead making a low-magic zone...
The Petty Kingdoms is a region consisting of hundreds of small states. Some are kingdoms, some are city states, some are large farming communities, some are duchesses and baronies and so on and so forth. Within a few miles the PCs might reach a new "country" with completely different rules and norms than the one they left behind. "What do you eat here? Humans ye say? Lets turn around fellas."