Complex sentence: Some estimates say there were over 13 million bison in Montana in 1870,1875 General Philip Sheridan pleaded to a joint session of Congress to slaughter the herds, to deprive the Indians of their source of food.
Split into simpler sentences: Some estimates say there were over 13 million bison in Montana in 1870. In 1875, General Philip Sheridan pleaded to a joint session of Congress to authorize the slaughtering of herds in order to deprive the Indians of their source of food.