What if there was no Sakoku period in Japan? What effects was this have in East Asia?
That sounds quite interesting!It would depend on how history progressed, it might lead to Japan remaining mostly the same in terms of foreign relations (IE remaining separate from everyone, though without the limitations that Sakoku involved) or it might turn into an Asian Britain, becoming the major industrial and economic center for awhile and founding a diverse colonial empire.
With that said, I've actually been on and off developing a concept which lead to this (basically the Shiba came out on top as the unifying clan/polity); so far the scenario I came-up with has been that Japan, instead of doing what they tried twice IOTL, don't try to conquer Korea or force the mainland to recognize them as Superior, but rather focus on development and into the Pacific, which leads to Japan controlling basically all the North Pacific islands (and a few south pacific ones as well), establishing a sort of 'British Raj' type dealie in the Indo-Malay archipelago (most of the direct controlled territories being the sparsely inhabited, but useful islands), eventually annexing some statelets founded by Japanese traders and explorers (either out of request, need or just because they're causing diplomatic headaches for Kyoto) and establishing some trading centers (that expand, though not massively) along the Northern half of the North American West coast and subsequently establishing protectorates in a few cases and allying with native states in others.