Hydrologically, the Stanovoy Range separates the rivers that flow north into the Arctic from those that flow south into the Amur River. Ecologically, the area is the southeastern edge of the Siberian boreal forest with some areas good for agriculture along the middle Amur. Socially and politically, from about 600 AD, it was the northern fringe of the Chinese-Korean-Manchu world. For a Chinese view of this, see Outer Manchuria and Hulun (Manchuria). In 1643 Russian adventurers spilled over the Stanovoys, but by 1689 they were driven back by the Manchus. For this, see Sino-Russian border conflicts. By the Treaty of Nerchinsk (1689) the two empires recognized the Stanovoys and the Argun River as their border. This remained stable until the 1840s. Following the voyages of Captain James Cook significant numbers of British, French and American vessels began entering the Pacific. They were followed by Russians like Grigory Shelikhov and Nikolai Rezanov who were mainly concerned with the new Russian colonies in Alaska. This raised the problem of naval defense of the east coast of Siberia and the possibility of using the Amur River as a supply route to the Pacific.