Short answers, pulled from the story.
The Japanese Satsuma Domain invaded the Ryukyu Kingdom in 1609 and turned it into a puppet state. This invasion led to the development of karate as a secret system of unarmed combat to survive under a regime that had banned the carrying of swords.
Ankō Itosu is known as the Grandfather of Modern Karate. In 1905, Itosu helped to get karate introduced into Okinawa's public schools, teaching it to children at the elementary school level.
In 1933, the Japanese character for karate was altered to a homophone, a word pronounced identically but with a different meaning. Thus, Chinese hand was replaced with empty hand to reflect the idea that the practitioner should be free from selfish and evil thoughts.
After World War II, Okinawa became an important United States military site, and karate became popular among servicemen stationed there. The martial arts movies of the 1960s and 1970s served to greatly increase the popularity of martial arts around the world.
The dō suffix implies that karatedō is a path to self-knowledge, not just a study of the technical aspects of fighting. It is a way of life, a discipline that requires dedication, perseverance, and humility.