There are several reasons for choosing Van Vernau's territory as a sacrifice.
First, it was located in the southern part of Blande, which means it is closer to the sea.
Because Ryntum's side took the initiative to ask for his island, Hugo realised their objective for making that demand.
They want his island for its strategic location to control the vital trade route in the Leviathan Sea.
Whoever controlled the island would wield significant influence over the flow of goods, ships, and commerce in the region. For Ryntum, it was a prize worth fighting for.
However, he couldn't afford to lose the island— it was his possession and a core piece of his family's legacy.
Hugo wasn't stupid. The only way to save himself was to give them something equivalent to or greater in value.
And Vernau's territory fits the criteria.
Secondly, Hugo plans to give two cities from Vernau's holdings to Ryntum.