Well, when I listed them, I wasn't trying to get 18, just brainstorming. I just was coming out with possibilities. Sorry about the other, though. I've been thinking about other things lately (like school) and must have forgotten about that update. I have checked them, but I guess I forgot about that. However, Miyoshi Nagayoshi, for what I thought, was a general under the Murakami clan. Unfortunately, I can't find any referances anywhere of where he may have split off from them.
This could just be an incident of where Firaxis has given credit to the more famous figure. Just so that everyone's happy, I'll list six more significant clans.
Five more tribes (Unfortunately, the 18th tribe probably IS the Toyotomi. The reason why I say this is that, although he was only Shogun for a short period, did a LOT of foolish things, and had a short living clan, he did provide a big enough distraction to let Tokugowa Ieyesu to escape from his Hojo captives):
Murakami (Well, we already know that this one's called the Miyoshi Clan, but I still think that it should be called this. The Miyoshi family were generals under them, and apparently had close connections, as I've found that the Murakami's appointed a Miyoshi shogun, so there had to be strong family ties if they trusted the Miyoshi's this much. The Murakami clan is famous for challenging the Uesegwa and Takeda clans towards the shogunate. This clan was one of the first successful families to acquire the title of Shogunate)
Saito (after looking back at this one, he was quite significant. Saito Toshimata was a rich oil merchant. From what I read, he is famous for his treachery and his daughter's marriage with Oda Nobunga. This, in effect merged this clan with the Oda's, so I didn't mention it the other day.)
Ashikaga (first to challenge the authority of the Shogun. This was slightly before the Sengoku period, but not much. They were absorbed by the Tokugowa clan. Just so that the next part desn't sound confusing, Tokugowa Ieyasu was captured by the Hojo clan, which ended his clan. However, he restarted it when he escaped to Toyotomi during a battle. It seems that the Hojo began to trust him, and he rised to the rank of general. He then inherited Toyotomi Hideyoshi's clan)
Toyotomi (This is the tribe that Tokugowa split off from. I didn't mention it before because of that. This tribe challenged China and Korea! Their failure to set up Shoguns over there, and that they ruled over the sea, led to their failure to keep them. However, they plundered lots of goods from both of these places)
Ishida (I guess I forgot to mention this one... Nicknamed the Western Army. If you're wondering who the Eastern Army was, then you're forgetting who won this war. This was one of the final two. He caused big trouble for Tokugowa when Will Adams sold guns to the Ishida tribe. )
Just thought that you'd be interested. Here's the legend of how the Japanese Islands were created, direct from one of my sources:
The Japanese home islands themselves came into being when the gods Izanagi and Izanami stood on the bridge of heaven and stirred the waters of the Earth with a spear. The drops of water that fell from the spear tip gathered together to become the islands of Japan. The pair then descended and raised the spear as the centre pole of their house. Japan had been created.
Izanagi and Izanami had children. Their first born was Amateratsu, the Sun Goddess, but like all families there were problems: Izanagi slew his second child, the Fire God, who had caused his mother, Izanami, enormous pain when he was born. Izanami fled into the Underworld in grief at this killing. Susano-o, their other son, was given to fits of temper. His violent behaviour included throwing thunderbolts across the sky, and he even threw a dead horse at Amateratsu, forcing her to hide in a cave. With the Sun Goddess in hiding, the world was plunged into darkness. Amateratsu was eventually tricked out of her hiding place by the sight of her own beautiful reflection in a mirror and a necklace of precious jewels
Susano-o did eventually make amends by slaying a great serpent with eight heads and tails. The serpent had a taste for young maidens and this, along with an equal appetite for sake. Susano-o used both to lure the serpent into a trap, then slew it once it was drunk! In hacking it to pieces, he discovered a sword embedded in its tail which he then gave to Amateratsu. This was the Ame no murakomo no tsurugi or "Cloud Cluster Sword."
As the first born child, Amateratsu inherited the earth and in time sent her grandson, Ninigi, to rule Japan. She gave him three gifts, the mirror, the jewels from the necklace and the "Cloud Cluster Sword" to make his task easier. These gifts from heaven became the Japanese Crown Jewels. Ninigi left heaven and ruled Japan, and the throne eventually passed to his grandson, Jimmu, who was the first earthly Emperor of Japan. He took the throne in 660BC on 11 February, a date which is still a public holiday in Japan. The current Emperor is a lineal descendant of this first Emperor.
In around 200BC, Emperor Sujin and his son Prince Yamato (later Emperor Keiko) are the agents of an important change in Japanese history. The nation at this time was composed of many clans, of which the strongest was the Imperial Yamato family. The Yamato (named for their home province in central Honshu) were one clan amongst many but they claimed the right to rule because they were descended directly from the Sun Goddess, Amateratsu. Sujin was the first Emperor to appoint four generals to deal with rebels in his realm. Each general was given the title of Shogun (which can be translated as "Commander in Chief" at this point in history). Yamato Sujin is a figure partly of myth and partly of history. He is the prototype of later samurai heroes: a skilled and noble warrior, harried and hunted down by his many enemies who although he comes to a tragic end eventually has a worthwhile death.
The Sengoku period was started when Emperor Antoku drowned with the "Cloud Cluster Sword". The loss of this artifact was detrimental to the ruling family, and they essentually became figureheads like the king and queen of England. The Daimos ruled Japan from this point, and Japan was segmented into individual "famous" clans who controlled the serfs within their territory.