Sinew backed bows
Anthropologists believe that archery arrived in Alaska and the Arctic at least six thousand years ago, eventually spreading to the rest of the US no later than 500 AD. In much of costal Alaska, wood is scarce and what is available makes for weak bows, which, in turn, makes killing large animals difficult. One ingenuous innovation to strengthen bows and to increase arrow speed was the creation of sinew-backed bows. Also known as cable bows, these weapons were made by using braided sinew running the length of the bow. A series of twists and hitches were used to strengthen the bow and increase its peak draw weight. Different regions of Alaska appear to have adapted this basic concept to create bows that suited their unique environments.
The modern compound bow traces its roots to Holless Wilbur Allen. In the early 1960s, Allen was experimenting with the creation of the first compound bow. At first, Allen tried sawing the ends off of a recurve bow and attaching pulleys, which created a crude block-and-tackle system. It didn't work well, and after four years of experimenting, he developed a system of cams and eccentric wheels in place of the original pulley system. He patented his design, and by the 1970s compound bows rose to dominate the field of archery. These bows featured increased arrow speed and reduction of peak draw weights. This allowed hunters to hold the bow at a full draw for extended periods of time, with the cams and wheels absorbing and storing the energy before transferring it back to the bow when the archer released the string.
Murdoch, John. 1884. "A Study of the Eskimo bows in the U.S. National Museum.” in Report of the United States National Museum for the year 1884 (Pt. 2 of the Annual Report of the Board of Regents of the Smithsonian Institution for the year 1884), 307–316, 12 pls.
United States patent office