I do not see Japan’s
Karafuto Prefecture, including the southern half of the island of Sakhalin, surviving the Second World War. Simply put, Karafuto shared the island with the
Sakhalin Oblast of the Russian Soviet Federative Socialist Republic of the Union of Soviet Socialist Republics. With an exposed border with a well-armed country that wanted revenge on Japan for its past victories against different Russian states, I see no prospect of Karafuto surviving. The
southern Kuril islands, now, might have remained Japanese had the international agreements leading up to the surrender of Japan been clearer about the disposition of these territories, perhaps especially if Soviets had not taken the islands.
If we go further back, it might be possible for Japan to acquire all of Sakhalin. It’s my understanding that some people in Japan wanted to acquire the entire island, not just the relatively warm southern half, but that the Russian Empire was reluctant to transfer the entire island while Japan was just not that interested in the north, and everyone just wanted peace to end an expensive war. (Apparently, at one point Sergei Witte was willing to give Japan the entire island if it dropped its demand for reparations.) I think it imaginable that a Japan that fared better in the Russo-Japanese War could well take the entire island. In this case, it would gain a territory that would be much more defensible against future attacks. If the rest of history proceeds as it did in our timeline, the Soviet Union may never be able to invade this all-Japanese Sakhalin from across the
Nevelskoy Strait, never mind the southern Kuril islands.
What will these northern territories look like? Adjacent Hokkaido, successfully colonized under the Meiji by Japanese migrants under the guidance of a new government that had access to the latest agricultural and other technologies of the West, provides an example of what might be possible. Karafuto’s population peaked at four hundred thousand before the Soviet invasion. I think it imaginable that this all-Japanese Sakhalin’s population might be significantly greater, well above a million. The oil, in particular, might be a potent driver for immigration, as might American military bases assuming there is a Cold War.
(The Soviet Pacific is going to evolve differently, with Japanese Sakhalin and the Kurils sharply limiting Soviet naval access to the open Pacific. Petropavlovsk Kamchatskiy may see more development, while Vladivostok may see less.)
Assuming that Japanese history continues to proceed more-or-less as it did in our history, these northern territories of Japan would probably be much richer and more populous than they have been in our history under Soviet then Russian rule. I see no reason to think that these islands’ retention by Japan would significantly alter the general direction of Japan’s development, with an economic boom lasting until the 1990s followed by a marked decline. Probably there would be government megaprojects intended to tie Sakhalin more closely to the other Home Islands, perhaps up to and including a tunnel linking the island and its transportation network to Hokkaido.
Thoughts?