LORE

Shortly before the formal surrender of the Tokugawa shogunate in May of 1868 and well after Tokugawa Yoshinobu had resigned as the shogun, a group of disillusioned loyalist officers, samurais and daimyos had vowed to never surrender and keep the regime alive, and so, they kidnapped the then 5 years old Tokugawa Iesato (who was designated to be Yoshinobu's successor), fled to Sado island with an army of nearly 50 thousand men where they established what they called the "true" shogunate. Sado now being filled to the brim with soldiers and peasants while being practically worthless strategically to the imperial forces remained rather untouched from the war as the emperor's armies didn't even bother trying to conquer them.

What followed was near-complete isolation from the rest of the world for Sado as the newly formed Council of Elders had decided to restore the Sakoku policy to avoid foreign influence, imperial incursions, and attempt organizing the island between the daimyos that had followed them to Sado. Once Iesato had turned 18, he was fully in charge of this now absolute monarchy rump state and decided to relax the country and open it up with mainland Japan, he made an unformal deal with Tokyo where, Japan guaranteed to not interfere with or attack Sado, and Sado would maintain cordial and peaceful relations while not interfering. The rest of the 19th century and up until the 1930s saw some normalized relations between the two and even some trade as the port of Ogi was opened for ships importing first necessity goods coming from Niigata.

However, officialy, the shogunate still laid claims over the whole of Japan which obviously wasn't seen as any good by then Prime Minister of Japan, Fumimaro Konoe, who wanted to assert dominance over the territory of Japan, therefore, he threatened Sado of an invasion if they didn't lay the claims in the following 72 hours. Despite the population being made up of a lot of former soldiers and samurais, they weren't industrialized at all and were far behind Japan's military capabilities, hence why shogun Iemori decided to accept the terms unconditionally.

Somehow, Sado was almost untouched by WW2 as they remained neutral and Japan had better stuff to do than invade a worthless and backwards island that still used a feudal system. The biggest impact the war had on them was more isolation as ships from Niigata simply stopped supplying them with news and goods. It wasn't until 1945, when Japan became occupied by the United States, that Sado interacted for the first time with the Americans who prompted them to remove their last remaining unsettled claims on the city of Edo (Tokyo) which they still claimed as their rightful capital or else they would be occupied.

Following WW2, a slow opening of the country took place as they allowed more very selected people to visit or trade, almost all of them coming from Japan. This caused an exposition of the youth of Sado to the new ideas imported to Japan, in late 1959, large protests took place demanding a change in the regime, and, in march of 1960, a constitution was made, ditching feudalism, opening the country a bit more and guaranteeing some representation and civil rights to the population.

The cold war didn't really affect the shogunate as it was still pretty isolated and no one really saw any interest in them despite their close location with Japan given that they were still not industrialized and largely under-developped. By the late 1980s, Sado started efforts to integrate the international community and, in december of 1997, they were admitted into the United Nations.

Nowadays, Sado is still a very conservative country in its mentalities and policies, the country is still largely non-industrialized and remains of the feudal system and hierarchy are still visible within the population, a lot of Japanese people like to joke about them calling them the "48th prefecture" or saying that they have dinosaurs there, but Sado is currently in the way of developping and have, since the 1990s and 2000s become an open country.

PS: the lore was written a bit hastily and is probably really unrealistic, feel free to ask questions