Kuril Islands, located between Kamchatka and the isle Hokkaido, often change its owner. Two countries alternate periodically in this activity, Russia and Japan.
  In 1855 Japan and Russia signed a non-aggression treaty in Shimoda. Its part was also the agreement about the division of the Kuril Islands. The so-called Northern territories, which consist of the Etorofu-to, Kunashiri-to, Shikotan-to isles and Habomai archipelago devolved to Japan. The other Kuril Islands spreading northeast up to the coast of Kamchatka were gained by Russia.
  In 1875 an agreement was signed in Saint Petersburg, according to which the whole Kuril archipelago fell to Japan in return for Sakhalin Island. Eight years earlier the tsar Alexander II sold Alaska to the USA for 7.2 million $.
  This is the end of the era when the Kuril Islands and other territories in this region were subject to trade. In the times to come they only changed hands as booty. Besides, it was quite common in the 20th century that borders changed often as a consequence of war conflicts.

  During the Russian-Japanese war in 1905, Japan beat the Russian Baltic fleet in the straits of Tsushima. The American president Theodore Roosevelt consequently mediated peace talks in Portsmouth. Russia then had to surrender the southern part of Sakhalin Island in favour of Japan.
  In 1945, after their defeat in WW II, the Japanese lost both Sakhalin and the Kuril islands including the Northern territories. But the further development was marked by the Cold war events. In 1951 a treaty was signed in San Francisco about the formal termination of antagonism between Japan and the allies. Japan officially waived the claims upon the northern part of the Kuril Islands.
  However, the year before the Korean War began and the USA made a commitment to protect Japan from communism. This was why the San Francisco treaty was not signed by the Soviet Union, and so the southern part of the Kuril Islands (i.e. the Japanese Northern territories) remained under its control. To this day Japan has been making claims upon the territory of these islands, which Russia as the successor of the Soviet Union refuses to acknowledge.