By this `` diplomatic document '' Russia came into possession of that section of Livonia which had still remained in Commonwealth control , and of Belarus embracing the counties of Vitebsk , Polotsk and Mstislavl . By this `` diplomatic document '' Russia came into possession of that section of Livonia that had remained in Commonwealth control , and of Belarus embracing the counties of Vitebsk , Polotsk and Mstislavl .