Many of these US servicemen took their newfound skills to the United States and established their own dojos. Many Japanese karate instructors were also sent to popularize the martial art in the United States.Robert Trias was the first American to open a karate dojo in the United States.
Joey Rhodes was one of the first karate instructors to transform point kumite (sparring) into full contact United States karate. As the captain of the Eastern Illinois University karate team, Rhodes transformed karate into a popular activity through his numerous invitational open style tournaments, clinics, and camps. Rhodes is the founder of Rhodes Karate Schools and started his training in 1968 with the Japan Karate Association. 
In 1946 Robert Trias, a returning U.S. Navy veteran, began teaching private lessons in Phoenix, Arizona. Other early teachers of karate in America were Ed Parker (a native Hawaiian and Coast Guard veteran who earned a black belt in 1953),George Mattson (who began studying while stationed in Okinawa in 1956), and Peter Urban (a Navy veteran who started training while stationed in Yokosuka in 1954).
Prior to 1946, most karate teachers outside Japan were in the Territory of Hawaii (not yet a state). Many of those teachers taught Kempo, to Asians and locals only — one such teacher was James Mitose. It was through Mitose that one style of Kempo (Kosho Shorei Ryu) was introduced to the world through William Chow, one of his black belts, who then went on to modify it and train Adriano Emperado, Ed Parker, Ralph Castro, and a host of other future grandmasters, some of whom brought the modified art to the U.S.
In the 1950s and early 60s several other Asian karate teachers began arriving in America to seek their fortunes, and to aid in the popularization of the art. They included Hidetaka Nishiyama, Teruyuki Okazaki, Takayuki Mikami, Tsutomu Ohshima, Richard Kim, Takayuki Kubota and Kazumi Tabata. Several Koreans also came to America in those days to introduce the Korean version of the martial arts (not yet known by the term taekwondo). They included Jhoon Rhee, Henry Cho, Kim Soo, and Jack Hwang.
In spite of the presence of these Asian instructors, karate was primarily spread in the early days by American-born teachers. They included Trias (called the “Father of American Karate”), Don Nagle, Parker, Mattson, and Urban, plus pioneers like Harold Long, Steve Armstrong, Allen Steen, Ernest Lieb, Pat Burleson, Chuck Norris and Joe Lewis.
The 1960s saw tremendous growth in karate’s popularity in the United States. By the 1970s there were even professional karate tournaments, a precursor to full contact karate and kickboxing.