The best scapegoat is something that already plagues this kingdom - preferably something that specifically engages in the kind of nasty crimes that undead generally don't commit (like crop destruction or mass arson). It works even better if you can specifically make your undead out of whatever menace that was. if you produce your skeleton horde by killing off the orc horde and using the skeletons as a garrison against more orc attacks, that's going to go a long way.