The buffalo’s demise (actually bison, but whoever heard of a bison-nickle) began with firearms and the introduction of horses to the plains Indians in the 1700's. It was hastened in the 1800's by the industrialization of the tanning process, by inroads made into the west with carts, steamboats, and railroads, and by the popularity of buffalo-hide coats in Europe. A robust trade ensued.
Most of the buffalo slaughter took place between 1830 and 1860. Undoubtedly, politics and the problem of the American Indian played a part.