What he is lacking is not ambition, but negotiations ability: during the last 500 years she has lacked the economic incentive, or the ability alltogether, to retake that land. With his coming, the difficulty and the cost necessary to military retake that place has only increased: her only choices would be to either acknowledge the new management, and get paid taxes for it, or deny his de facto ownership, and get only pains in the ass for it.
Or hope the new owner is dumb enough to give it away for free, which apparently is the case here...