The exact origins of some Japanese martial arts can be difficult to pin down. There are some important concepts about the external influences that can help us understand where these systems came from.
First, it’s important to understand the concepts of koryu and gendai. Koryu (literally old school) martial arts, in Japan, predate the Meji restoration (around 1866).Koryu styles include Japanese jujutsu, kenjutsu, schools of iaido, sumo, archery and other arts. Gendai martial arts post-date that era and include Judo, Aikido, Karate, and others.
Any country which has experienced warfare will ultimately develop some systems of armed and unarmed fighting. Human beings who fight one-another will discover or invent methods for more efficiently doing battle. This is simply inevitable. Every human body behaves in predictable ways, has limitations on it’s movements, and can be damaged the same way. Because of this factor, all martial arts have similarities. This is why it can be difficulty pinpointed imported techniques.
In Japan, and many other countries fighting systems were passed down among families. At one time, there were over 1000 documented systems of jujutsu in Japan. Very few of these remain.
For much of it’s history, Japan was insular, locking out all foreigners by force. However, the important influences of China and Korea in the development of Japanese martial arts are not to be underestimated. China, in turn, undoubtedly drew martial arts influence from places like India, Persia, and even Greece. So, one can find techniques in the martial arts of India in the martial arts of Japan.
All martial arts are necessarily influenced by the environment, the enemy, the landscape, the culture, and religion. In early Japan, the samurai were the warrior class. The samurai were used to organized battle on a field (much like European knights). Their battle arts included the use of horses, bow and arrow, the sword, etc. Jujutsu, the unarmed component of the samurai arsenal was designed for fighting armed and armored opponents. Jujutsu relies on throws and joint locking primarily because striking armored opponents was less effective.
Karate, on the other hand, cam from Okinawa but originated with Chinese arts. At the time, the Okinawans had been disarmed by the shogunate. Their style relies primarily on pugilism. Karate weapons frequently derive from farm and fishing implements.
Spiritually, the people of Japan have gone through periods where the country as a whole seemed to embrace pacifism. Out of this, and the quest for personal betterment the “do” arts evolved. When the name of an art ends with “do”, such as karate-do, aikido, judo, you can safely assume that it’s undergone a transformation from a combat art to one aimed at personal or spiritual development. “Do” in Japanese means path or way. This isn’t to say that you can’t use judo or karate-do in a combat setting, it’s just a switch in emphasis.
To denote a combat oriented art, the ending “jutsu” is typically used. Jujutsu is to Judo as Kenjutsu is to Kendo. There is such a thing as karate-jutsu, and aikijutsu, and iajutsu. These are rarer arts today. Jutsu can be translated as “art” or “combative art”. It’s one of those characters in Japanese that has many layers of meaning.
There are some rarer indigenous arts of Japan such as ninjutsu or ninpo and the martial arts of the Yamabushi (mountain ascetics). From what I’ve seen, these arts have much in common with styles of jujutsu, but may combine arts like espionage, poisoning, and some unique weaponry. Some scrolls I’ve seen from various ninjutsu schools reference Chinese arts – so there are definitely some influences there.
The problem with nailing down the historical origins of many arts is that they may pre-date written records. It also may be true that families wished to keep their arts secret for ancient OPSEC.