Both the differences and similarities are vast. The main difference is the basic philosophy and/or religion that is woven into the fabric of the styles ... In the east, they had Hindu, Taoist, Buddhist, Zen, and Shinto as the major influences in the ways of thinking, and this set the framework for the concepts and strategies that led to the motion patterns ... In the west, they had the various pantheons of Egypt, Greece, Rome, Carthage, the Norse, the Persians, and the Arabs, which eventually became just Jewish, Christian, and Muslim. While China had lots of metal, Japan and the surrounding islands had very little, so China developed a diverse set of metal blades while Japan developed a diverse set of misc. wooden weapons, some with woven fabric cords, as well as small metal or ceramic objects such as throwing stars. The Arabs had the math and physics to make crossbows, catapults, and ballistas, as well as fragile clay pots with flammable oil ... the British isles had strong hardwood which became the famous English longbow, pikes, spears, and misc. pole-arms, which differed from the Asian bamboo pole-arms and their short bows made from many thin ply strips of different woods bound together.

At their core techniques, they are very similar, provided they are actually "martial" in application. Once an MA has been sportified or ritualized, things can change drastically depending on the rules being used. Non-sporting Western arts tend to be VERY weapon-based. Even Savate (French kickboxing) can include cane and staff fighting in its cirriculum. There is an article entitled "Kindred Spirits: The Art of the Sword in Germany and Japan" that details the striking similarities between German and Japanese swordsmanship. It might be useful to you.