From The Grey House:
For the past ten years Vincent Grey and his people had been traveling to various cities in the United States, trying to discern which city most needed their attention. For the most part, Vincent didn’t interfere when vampires roamed a city. If they lived their lives peacefully with humans, nothing needed to be done. Every so often, he would find a city with vampires that desperately needed to be reined in, like San Francisco. The vampires who were in semi-control here were allowing atrocities to be committed and laughing about it, while the Slayers moved in, making it hard for those like him to be able to live. His people started coming here in stages for the past five years, assessing the situation and plotting.