Complex sentence: This border was challenged by the British and the United States, which ultimately resulted in the Russo-American Treaty of 1824 and the Russo-British Treaty of 1825, which established 54 ° 40 ′ as the ostensible southward limit of Russian interests.
Split into simpler sentences: This border was challenged by both Great Britain and the United States, which ultimately resulted in the Russo-American Treaty of 1824 and the Russo-British Treaty of 1825. These established 54 ° 40 ′ as the ostensible southward limit of Russian interests.