Oooh, I was just checking out
Pacific Overtures today. Anyways, perhaps we should start from the top. Japan did not just have contact eight eh outside world through Nagasaki. They also traded with the Ainu and the Koreans. Thr Satsuma also threatened their way into the RyuKryu islands, forcing them to act as puppets. This was partially to trade with China through them. The people of those islands could not trade with those outside the Chinese Imperial system, which led to awkwardness as people wouldn't sell foreigners stuff. One slightly unhinged minister had to drag sacks of food from people, leaving money behind before going back to the temple he was squatting in. At the end of his many years there he was given all the money he paid, as it had constantly been confiscated. But yah, the Japanese very much desired foreign trade. Just in a way that kept the profits for the lords. If that meant keeping thr Dutch in a small island, and making them store all their goods in Japanese warehouses (which th Dutch could not take the stuff back form, and they had to trust the Japanese to sell it) then so be it. Once when they were planning on threatening the Dutch they actually asked some other lords to make sure they could increase imports from Korea, so that there would be little actual change in the volume bought or sold.
The exclusion policy was mainly a matter of security. For the Shogun. And some lords. and the council that took over from the shogun when he became more like a figurehead, if the book Shogun is to be believed. It was kind of like how people form samurai families were forbidden to participate in commerce. The social hierarchy would be kept in place and, and all sorts of wasteful policies, such as making people live as hostages using exhorting amounts of money for stupid fashions, kept people weak. The Tokugawa shogunate did start there reign by taking a third or half the land from one of their allies. If they treat their friends like that, why would they be any kinder to the needs of the common folk? Plus I suppose part of the reason for seclusion Macau have been because of th Japanese losing. The war in Korea didn't go great, and the achinese were very angry t them for their pirate raiders, though I think the Chinese scrapping their own fleets helped make them vulnerable to them.
Anyways, assuming Japan DID stay isolated until, say, one hundred years ago.... Communist revolution. But so many strains to choose from. Maoism, a bit of Juche, maybe we get Hoxha... Sure, it might turn into a hermit state once more, but it is what it is.