When the chaos from Manohar's death and the Dead King's threats reached its apex, the members of the Undead Courts attacked every city where one of their branches was located.
The Dusk, Dawn, and Night Court had collaborated to turn as many Thralls as possible into undead and to raise armies of lesser undead exactly for that moment.
Every city had cemeteries and slaughterhouses, providing them with everything they needed. The attack was swift, brutal, and bloody. To the citizens of the Kingdom, it looked like another attempt of conquest but the undead's only aim was to brew fear.
They didn't attack strategic objectives or places that would give them the upper hand in the long term. They focused on the most populous areas, killing in the most cruel and terrifying ways possible.