They arose in a natural geographic and economic expansion that was driven by the lucrative earnings available in the North American fur trade, in the wake of the various 1806–07 published accounts of the Lewis and Clark expeditions' (1803–1806) findings about the Rockies and the (ownership-disputed between the United States and the British) Oregon Country where they flourished economically for over three decades. By the time two new international treaties in early 1846 and early 1848b) the 1848 treaty formally ending the Mexican–American War.</ref> officially settled new western coastal territories in the United States and spurred a large upsurge in migration, the days of mountain men making a good living by fur trapping had largely ended. This was partly because the fur industry was failing due to reduced demand and over trapping. With the rise of the silk trade and quick collapse of the North American beaver-based fur trade in the later 1830s–1840s, many of the mountain men settled into jobs as Army Scouts or wagon train guides or settled throughout the lands which they had helped open up. Others, like William Sublette, opened up fort-trading posts along the Oregon Trail to service the remnant fur trade and the settlers heading west.