mapsontheweb:

Seafloor temperature in the Western Pacific.

Yeah one of the weird subtleties of history is the Sea of Japan is just really cold, like Baltic or Arctic Sea cold, that dampened trade across it (it was dominated by pirates at several points, really)

And sailing on the outside coast of Japan you ran a risk of getting caught by powerful currents and dragged out into the empty middle of the Pacific

And Japan is such a steep mountain range there’s like no good internal waterways (except Lake Biwa, which is mountains away from either coast tho)

A very important thing about Japan is for most of its history it relied on overland transport