User blog comment:AYET/Yonko Territorial Claim/@comment-3125914-20130523040210

I never thought of the New World territory being equally divided. Like DSP said, the Yonkos most likely visited islands and just claimed them. They would also fight for certain islands from time to time. The equal dividing might be a posibility as well, and I tend to think that the 2nd model is most likely the way it would be done.

However, in both cases, after Whitebeard's death, most of his islands would fall in the hands of other Yonkos. Some of them might be saved and still protected by the surviving WB pirates, thus they are not part of a Yonko's territory anymore. As for Blackbeared, he might want to claim something as well, but I don't think his influence is as wide-spread as Big Mom's for example.