Japan's military planners had considered seizing Sakhalin from the war's earliest days, but the Imperial Japanese Navy vetoed the idea, wary of overextending. The calculus shifted on May 27, 1905, when Admiral Togo's fleet annihilated the Russian Baltic Squadron at the Battle of Tsushima, eliminating any naval threat in the region. On June 7, U.S. President Theodore Roosevelt met with Japanese diplomat Kaneko Kentaro and endorsed the invasion. Roosevelt's reasoning was blunt: only the threat of losing sovereign territory would bring Tsar Nicholas II to the negotiating table. Japan and Russia had once shared Sakhalin, but Japan had traded away its claims in the 1875 Treaty of Saint Petersburg in exchange for the Kuril Islands. Now it intended to take back what it had given up -- and more.

By 1904, Sakhalin was less a strategic outpost than a dumping ground. The island's 30,000 inhabitants included roughly 4,000 Ainu, the indigenous people whose fishing villages predated both Russian and Japanese claims. The rest were largely prisoners, deportees, and the bureaucrats who oversaw them. The island was notorious for its brutal winters, its isolation, and the corruption of its administrators. Russia had invested almost nothing in its defense. The nominal garrison of 7,280 men under General Mikhail Nikolaevich Lyapunov -- the lawyer-turned-commander -- consisted mostly of conscripted farmers, hunters, and political prisoners who had never fired a weapon in anger.

The Japanese struck on July 7, 1905, landing their main force between Aniva and Korsakov on the island's southern tip without encountering resistance. A secondary force landed closer to Korsakov and destroyed a Russian artillery battery after a brief skirmish. Korsakov fell the next day after seventeen hours of fighting by a 2,000-man Russian rearguard that set the town ablaze as they retreated. The Japanese pushed north, taking the village of Vladimirovka -- present-day Yuzhno-Sakhalinsk -- on July 10. Colonel Arciszewski attempted to hold a defensive position but was outflanked and driven into the mountainous interior, surrendering with his remaining men on July 16. Two weeks later, on July 24, a second Japanese force landed near Alexandrovsk-Sakhalinski in the north. General Lyapunov's 5,000 northern troops, outgunned and outmatched, surrendered on July 31.

The numbers tell the story of a one-sided campaign. Russia suffered 181 dead and 3,270 captured; Japan lost 18 killed and 58 wounded in the southern operations alone. The low Russian resistance reflected not cowardice but despair -- soldiers who were prisoners before the war began had little reason to die for an empire that had exiled them. At the Treaty of Portsmouth, mediated by Roosevelt in New Hampshire, Russia ceded the southern half of Sakhalin below the 50th parallel to Japan. The territory became Karafuto Prefecture, and the Japanese would govern it for the next four decades, building railways, towns, and a colonial administration that reshaped the island's demographics. When Soviet troops reclaimed all of Sakhalin in August 1945, they found an island that was, in many places, more Japanese than Russian -- a legacy that persists in place names, railway gauges, and the Korean diaspora that remains on Sakhalin to this day.