JohnDThompson 

SunTour's great innovation was the "slant pantograph" rear derailleur, which allowed the pulleys to closely follow the profile of the sprocket cluster, which resulted in uniformly smooth, fast, and reliable shifting. SunTour's patent on the slant pantograph expired in the mid-80s, and Shimano immediately incorporated it into their own derailleurs (today, almost all rear derailleur use a slant pantograph). The new Shimano derailleur also featured the "Shimano Index System" (aka "SIS"), the first really reliable indexed shifting system. Shimano heavily marketed this system to OEMs and consumers, and required that OEMs wanting to spec SIS in their products to spec a fully Shimano drive train. This destroyed not only SunTour's slice of the market, but many European component manufacturers as well. Shimano came out on top, and the rest of the component manufacturers either went out of business (SunTour, Simplex), were bought out by other companies (Sachs/Huret), or shed a large portion of their product line (Campagnolo) in order to stay afloat.