Although Japan once lost its sovereignty over Sakhalin as a result of unequal treaties signed from the end of the Edo period to the early Meiji period, the southern area below latitude 50 degrees was reverted to Japan after the Treaty of Portsmouth in 1905 (it was originally defined as the inland by the Common law and was treated as a quasi-territory.
樺太は、幕末から明治初頭にかけての不平等条約で一旦喪失したが、1905年調印のポーツマス条約により、緯度50度線以南が日本領に復帰した（もともと共通法で内地とされ準内地的扱い。