This is the most common misunderstanding regarding the historic roots of Karate. Originally, Karate was written as 唐手 ("Chinese hand") due to the influence of kung fu on the native Okinawan fighting techniques that Karate originated from, since merchants and sailors from Fujian Province were traveling back and forth from Okinawa. This was later changed to 空手 ("empty hand") in 1929 to better reflect the philosophies of the art.
Karate, like jujutsu and judo, most likely came to America through two primary paths: Japanese immigrants to Hawaii and the mainland, where it stayed largely inside the Japanese American community, although to a lesser degree in Hawaii, and by specialized study by members of the police and the military. It would be safe to say that the biggest boost to the popularization of karate in America came with the American military occupation of Japan after World War II; once American soldiers had assimilated the discipline, they returned with it to the States and began to disseminate it.
Like most martial arts active in Japan, Karate made its transition to Karate-Do at the beginning of the 20th century. The Karate-Do does not, contrary to its Chinese relatives, include the use of weapons. Any weapons used are strictly within the Okinawan tradition, kobudo, the use of modified farming tools and common implements as weapons, since 'normal' weapons were banned in Okinawa. Within Karate and Karate-Do, there are a multitude of different ryus (styles or schools), the most renowned are Shotokan (pine wave) and Kyokushin (ultimate truth). Other mainstream styles are Seido, Wado Ryu, Goju Ryu, Uechi Ryu, and Shito ryu.
Shotokan style Karate is characterised by deep, long stances to provide stability and powerful movements. At the other end of the spectrum, Wado-Ryu (way of peace) prefers quick and subtle body movements (known as 'tai sabaki') to evade attacks and swift counter attacks. The Wado-Ryu style was introduced to the west by Sensei Tatsuo Suzuki.
Karate is a hard martial art and emphasises striking techniques (i.e. punching and kicking) over grappling. Karate can be divided into two major parts, kumite and kata. Kumite (組手) means sparring and develops from well defined forms to the free form named randori. Kata (型) means forms and is a fight againt imaginary enemies, it is a fixed sequence of moves.
In Kumite, two opponents wear different coloured belts (typically red and blue) and fight until a clean point is scored as indicated by one of two seated judges by coloured flags or seen by the standing referee. At this point sparring is stopped and the point is awarded. Points systems vary but in general a half point (wazari) is awarded for a single punch or for a kick to the body. A full point (ippon) is given for an attack such as a head kick, any attack following the opponent being taken to the ground or a combination techniqure (renrakuwaza).
In Kata points are awarded by five seated judges similar to either gymnastics or ice skating tournaments depending on the quality of the performance. A good Kata performance should perform all the movements correctly but also show a personal interpretation of the movements through one's variation in speed. When Kata is performed as a team (usually of three), it is also important to match the timing of techniques as closely as possible.