Many articles have been written about the history of saddles and the care of saddles. On this very site "HorseDiva," wrote a beautiful article spelling out the history and care of saddles.
Saddles of all types have been used for thousands of years all over the world. There have been saddles found in Siberia, that dated back to 500 and 400 BC. Early saddles were often pads with a girth strap, that evolved over the years into solid-treed saddles made of heavy felt covering a wooden type frame. Then down through the ages different designs of saddles were invented depending on the use intended for the saddle. And so the English and Western types of saddles were invented and molded to fit the horse and its rider.
The English type saddles are used in casual riding and hunt-seat, show jumping and dressage, horse racing and polo matches, etc.
The Western saddles were designed for use on cattle ranches, however, now are used for casual riding and rodeo events, barrel racing and trail riding.
The Military saddles were used by the Royal Mounted Police and army personnel, in Britain and Canada, Australia and New Zealand, South Africa and by the United States Cavalry. In 1850 the McClellan saddle was made by George B. M Clellen, and used by the cavalry and for ceremonial parade mounted troops in the U.S. Army as well.
There were many other different types of saddle designs created for different purposes, such as Side saddles and Trick saddles, Endurance riding saddles and Pack saddles, Police saddles and the McClellin, Double Seat and Treeless saddles, Flexible and Bareback pads.
The most interesting part of saddle design is the ability to see one made. Go here and watch an English saddle being made from start to finish: http://www.youtube.com/watch?v=onelxEOo_K8
Then go here and watch how a Western saddle is made from starting with a pattern to the finished product: http://www.youtube.com/watch?v=WJpme2k6xvg
One other example of saddle making can be found in these step-by-step pictures in the creation of a saddle: http://www.freckerssaddlery.com/making_saddle.php
It is one thing to throw your saddle up on your horse in getting ready to ride, but quite another adventure to now look at your saddle and see the workmanship and design of the craftsman who put together that saddle with various tools and his bare hands.