The Great Hakurei Divide is the border that separates Japan and Kozan. While it today exists as an international border, it wasn’t always this way. The border’s roots go all the way back to the Edo Period.
Many people in Japan fled to Kozan during Japan’s long period of bloody civil wars. After the Tokugawa Shogunate declared victory and established the final feudal military government in 1603, many people in Japan began emigrating east to Kozan in search of new opportunities. This was especially true following the Siege of Osaka when many people fled to escape the shogunate’s control. This caused a brain drain in the Japanese population after people kept fleeing Japan for Kozan.
Japan and Kozan had no physical barrier separating the two countries. Japanese could simply swim across the invisible line to travel to Kozan and be free. However, when the Sakoku policy was enacted in the 1630s, that loophole closed when the Japanese woke up to swordsmen guarding the border to Kozan. Unannounced, both the Tokugawa Shogunate and various workers from Western Kozan began building kilometers of spikes through that barrier to keep their people in to build political stability. They were building the Great Hakurei Divide, named for the Old Hakurei Shrine in present-day Horudika Canal.
As a result of Sakoku building that barrier, travel outside Japan, alongside foreign influence, became strictly regulated. Nobody was allowed to leave or even enter Japan unless they met strict criteria and those who didn’t faced a nearly impassible barrier complete with guard towers. Guards were given orders to shoot and kill anybody who tried to cross the barrier illegally. That’s how it remained for two and a half centuries.
There was another loophole in Hokkaido where people could simply get into Kozan without fears of being shot and killed by the border guards. That loophole closed in 1703 when the Kozanese continent split into two brand new countries, being democratic Eastern Kozan and communist Western Kozan. The western part of the country bordered Japan, specifically.
Change was made when the Americans forced Japan to open themselves up to the world. Freedom to travel was one key demand, and anybody who wanted to leave Japan could and come back. Right around the same time that Japan began to loosen their border, the neighboring Democratic Kingdom of Western Kozan also began to loosen their borders. After the Meiji Restoration was complete, Kozan was reunified with Western Kozan dissolving into the Federal Kingdom of Eastern Kozan.
Over the course of the Sakoku policy that generated the Great Hakurei Divide, nearly 900 people died trying to cross the Great Hakurei Divide. That fear dissolved after the restoration, and as of today, it is named as the land border crossings in Kozan to Japan. As of today, more than 35 million people cross the divide each year from trips to the other country, mostly situated in Western Kozan.