I would have to say the most popular non-japanese native martial art would have to be karate. Karate is from Okinawa which is currently part of Japan, however Karate as an art was created and practiced before the islands became part of Japan. The mainland Japan was for the most part ignorant of this art until Master Funakoshi brought it over and popularized it around 1920s.
@callsign taikiken is actually off shoot of Yi Quan which originates from Xing Yi Quan. It has elements that are similar to taichi, but doesn't share a direct lineage.
Boxing and wrestling are pretty popular, comparatively. The Japanese also have a variation of T'ai Chi (Taikiken), though I believe it might be called a hybridized martial art. Similarly, Shorinji Kempo might be called a "Japanized" Chinese martial art; the founder studied martial arts in China in the early 20th Century and brought the teachings back to Japan.
@ jay kas karate is considered a Japanese martial art... it came Ryuku Islands which is now Okinawa Ryuku in Okinawa means hand... which karate is based from Fujian white crane.. Japanese has had martial arts in samurai which is even older then all others even aikido comes unarmed samurai moves created by one teacher who is considered the last true modern samurai.. knowing that the Japanese dont ban any sport they do all martial art.. from Chinese wushu to tai kwon do and etc... martial arts is no longer a race thing or a region thing its what people take and then teach to others...
Brasilian Jiu Jitsu has become immensely popular in Japan in recent years. Although it comes from Japanese martial arts lineage anyway.
Maybe I try to know love but its tough in martial mind you should I am not japat or japef or japanese but so the thing is google nothing on anything but japan martial.
Boxing and catch wrestling are the only western ones I know.
What are the most popular martial arts that are not naive to Japan?