More art from Brother Casius image - Warhammer 40K Fan Group

They pretty much where from the start.(samurai looking armor, Katana, caste system, honor-bond culture etc.)

Not really they where typical Elf culture in space. Samurai culture in History before the Meji restoration, not the stuff you see on TV stereotypes, is far from what Eldar do. the Bakufu/Shogunate would not interfear much with other people and would try to isolate themselves completely. They would only trade with the Dutch because they helped them before and where thus semi trusted (only semi). Infact the the Bakufu would kill off their own people by if they suspected them being Christian Converts, something the Eldar would never do.

The Tau are very much like the Meji Restoration Japan without the racist undertones of superiority. Same Co prosperity Sphere/Expansion Sphere stuff. Mix of old and new cultures and forcing others to live like them.

A more accurate and longer comparison would take to many character as I'm already dangerously close to 2000.

ps:
Just like the Japanese beating the Russians in a naval war, as a relatively new Nation on the Colonial powers list. So did the Tau very quickly grow (compare to the other races) and in very short time became a power to be reckoned with.

They used new tactics or tactics they learned from others, including the older races. Incorporating technology from older races on a very fast rate. They investigate and improve this technology.

So really they are a lot like the Meji Restoration Japanese but without the racism that came by later in that era of history. Including carrying a Katana, that is more used as a ceremonial sword of honour and to kill yourself with (or execute people with), then in actual combat. Another nice note, Japanese naval ships during first few years of the Second World war had guns far exceeding the firing range and power of allied ships ;). Sound familiar? hehe.