日露和親条約
The 1855 Treaty of Shimoda acknowledged that both Russia and Japan had joint rights of occupation to Sakhalin, without setting a definite territorial demarcation. As the island became settled in the 1860s and 1870s, this ambiguity led to increasing friction between settlers. Attempts by the Tokugawa shogunate to purchase the entire island from the Russian Empire failed, and the new Meiji government was unable to negotiate a partition of the island into separate territories. In the Treaty of Saint Petersburg (1875), Japan agreed to give up its claims on Sakhalin in exchange for undisputed ownership of the Kuril Islands.