Our story begins in the ninth century, on a small collection of island nations that would become known as Japan. It was not Japan as we think of it today, as at this time the island was dotted with countless, independent kingdoms that were connected through complicated political and economic relationships akin to the feudalism of the early Middle Ages in Europe. The ruling class were the land owning lords, known as Daimyos.
Daimyos were faced with a constant threat of warfare, and to defend themselves they hired mercenary warriors to man and lead their armies.
Most of the warriors during this period were horsed archers - the bow was the pinnacle of military technology and archery was considered the most important skill for a warrior to have. These hired warriors were given privileged status by their local Daimyo in exchange for their service and over time, this lead to the establishment of these warriors as a noble class. These fighting nobles became known as Samurai.
As smaller kingdoms were absorbed by larger neighbors, warfare was held on a larger and larger scale. The importance of raiding forces like horsed archers was reduced and infantry became more important. Samurai began to fight with sword and spear as well as the bow. Some time after 900 A.D. all Samurai began to carry swords and were primarily sword fighters.
By the 1100s Samurai were a full warrior culture, and had become the ruling class of Japan; all Daimyo's were Samurai. As a noble class, Samurai were part of a very small percentage of people that did not rely on growing their own food to survive. They lived off food grown by others, giving them free time to perfect their craft: warfare.
Samurai that survived to old age would teach their successful skills to others at fighting academies, to which Samurai would send their sons to learn the ways of war. Over the next few centuries, these academies sprang up all over the dozens and dozens of nations that covered Japan. One of the skills a young Samurai would learn at these academies was the close combat are of Jujitsu.
Jujitsu developed as an unarmed martial art in a culture where basically everyone was armed, so the first goal was to deal with an attacker's weapon. Samurai would train to defend against swords, spears or knives. While strikes targeting the eyes, nose, groin and other vital points were incorporated, striking was not the focus of Jujitsu because Samurai armor would negate their effectiveness.
The nations of Japan had relative peace under the rule of military dictators known as Shogun and each nation had its own army of highly trained Samurai. But as the power of the Shogun slowly weakened, tensions between rival nations grew.
In the mid 1400's the powder keg that was Japan finally exploded into all-out war and for the next 200 years Japan would be embroiled in almost constant warfare. The Samurai were on the front lines for all 200 years of these wars and during this time Jujitsu experienced a trial by fire.
In battle, Samurai would take down armored enemies, when opportunity presented, with an array of trips and throws. Normally these would be used after a clash of swords to gain a lethal advantage. Once the dominant position was attained, the victorous Samurai would quick dispatch his vicitim with anything from his sword, to eye gouges, to the fallen man's own knife.
Here is an example of traditional Jujitsu, from the Takenouchi style:
竹内流柔術・こしのまわり小具足 - Takenouchi Ryu Koshi-no-Mawari Kogusoku (via ericspinelli)
While this is an excellent example of the actual art, this demonstration doesn't covey the speed and violence that Jujitsu brought to a sword fight. The video below is of a takedown technique very similar to ones found in Karate and Jujitsu, but it is in fact a recreation from the manual of 15th century German Sigmund Ringeck and is not Jujitsu. Medieval knights developed similar techniques because they to faced armored opponents, against whom punches and kicks would do little. Again it is a similar technique that conveys how it would be incorporated into a fight.
Overleg Throw - Ringen am Schwert ("Wrestling at the Sword") (via vaingloria)
As the period of intense war drew to a close, the 1700's became a golden age for the Samurai. Major warfare was rare, and as a result the martial arts flourished as mass amounts of Samurai did not die in battle. Schools sprang up and techniques evolved and developed.
Despite translating as 'art of softness' Jujitsu was a desperate art of survival that used anything at its disposal. Many techniques used blades, chains, biting, eye gouging or just pure brute strength to gain an advantage. That said, the most universal techniques operated on the principles of using momentum and leverage to defeat enemies rather than strength.
A fantastic example of Jujistu technique from the early 1900s that worked on these principles of using momentum to throw attackers.
"Textbook of Ju-jutsu" (1905) re-animated (via BartitsuSociety)
Despite this period of peace, political divisions still fragmented Japan. Schools in different nations or different islands would not have a great deal of contact and would develop their own styles, or Ryu. Representatives from different schools would test their martial skills against one another in duels to the death. Schools focused on different combination of weapons and different approaches to Jujitsu.
Some Ryu focused heavily on using Jujitsu in conjunction with other weapons. For example, in this clip from the Last Samurai Tom Cruise is sparring with an actor who is a practicer of Naginatajutsu, which uses a large slashing spear. The Japanese actor shows off two takedowns and a twisting leg lock.
Some schools of Jujitsu did develop techniques that involved being on one's back. Here is a video that shows something close to early guard work.
It is very important to note that working from the back would not have been common for Samurai. In battle, any Samurai who was thrown and was fortunate enough to retain his awareness would not be able use anything close to a modern guard. Instead it would be a desperate scramble back to the relative safety of their feet, all the while fighting off his attacker's attempts to stab through the gaps in the armor.
The Samurai were the dominant force in Japan but in 1853, the world of the Samurai was rocked when Commodore Matthew Perry of the U.S. Navy brought his steam-powered warships armed with modern cannons into Tokyo Bay. The result was the awakening of the Japanese people from their self-imposed exile. This would mark the beginning of the end for the Samurai and Jujitsu...
Turnbull, Stephen. War in Japan: 1467-1616. Oxford: Osprey Publishing, 2002. Print.
"05 Samurai Legacy." Human Weapon. History Channel. 17 Aug. 2007. Television.
Kano, Jigoro. "Jujutsu Becomes Judo." The original Judo Information Site
Nagaki, Kosuke. "Randori and the unification of Jujitsu disciplines by the Kodokan." The original Judo Information Site.