Arctic Horizon is the fourth province of Stage 1 of the Arctic Future, accessible (along with Aurora's Dale) after taking control of Iluliaq to the east. However, taking control of Arctic Horizon does not in itself unlock any other provinces.
If previous sectors acquired by negotiation:
My company was in the Arctic first. But I am willing to trade. Are you?
If at least one sector taken by force:
My company has acquired this valley quite legally! We will defend what is legally mine!
My mercenaries will defend what's legally mine!