A whistleblower at Russia’s Federal Security Service (FSB) shared with Newsweek a leaked letter that claimed Russia was “quite seriously preparing for a localized military conflict with Japan” in August 2021. Russia’s propaganda machine was also initiated, with a huge push to label Japanese as “Nazis” and “fascists.”

“Confidence that the countries would enter the stage of acute confrontation and even war was high. Why Ukraine was chosen for war in the end [the scenario was not changed much] is for others to answer,” they wrote. Russia launched a full-scale invasion of Ukraine in February 2022.

The plans for war with Japan may have been related to a longstanding territorial dispute concerning the strategically important Kuril Islands, which are occupied by Russia but claimed by Japan.

Russia and Japan previously fought in what is now known as the Russo-Japanese War of 1904-1905. The war was decisively won by the Empire of Japan, delivering what was then a shocking defeat to the Russian Empire. The conflict was fought over the countries’ rival expansionist ambitions in China and Korea.

The war began following the refusal of a Japanese offer to limit its ambitions to Korea while allowing Russia to take territory in China. On February 8, 1904, Japan launched a surprise attack on Port Arthur, an area of China that had been leased to Russia after being previously occupied by Japan.

Russia discounted an early Japanese proposal for a ceasefire, wrongly believing that its superior navy would eventually defeat Japan with ease. Russia went on to lose a series of battles fought on land and at sea. The war finally ended with the September 5, 1905, signing of the Treaty of Portsmouth, which was mediated by U.S. President Theodore Roosevelt.

There were up to 120,000 estimated Russian deaths and as many as 86,000 Japanese deaths as a result of the Russo-Japanese War. Historians say that Russia losing the war had a long-lasting impact on the world.

“Russia’s humiliating defeat in the Russo-Japanese War of 1904–1905 had profound effects,” a 2016 paper published in the journal Foreign Policy Analysis said. “Domestically, it accelerated revolutionary discontent in Russia and enhanced Japan’s national image as a modern state.”

“Internationally, it shattered long-standing beliefs in European military dominance, triggered a major loss of prestige for Russia, removed any doubts about Japan’s status as the newest great power, and redefined the balance of power in the Far East,” it added.

Scholars believe that the Russo-Japanese War also “set the stage” for World War I and World War II, with some referring to it as “World War Zero,” according to History.Com.

This month, Kremlin propagandist Vladimir Solovyov compared Russia’s loss in the Russo-Japanese War to the far more recent retreat of Russian soldiers from Kherson, Ukraine.

Russia, as part of the Soviet Union, was among the Allied forces to defeat Imperial Japan and other Axis powers in World War II.

In August 1945, while the U.S. military was dropping atomic bombs on Japan, the Soviet Union separately invaded a Japanese-controlled area of China and captured the Kuril Islands, which have remained in dispute since.

The FSB, in August 2021, declassified information concerning the brutal torture of Soviet citizens by Japanese special services during World War II.

The FSB whistleblower suggested that this was part of an “information campaign against Japan” that could be used to help condition Russians for the planned 2021 attack.

Updated 11/25/22, 5:30 a.m. ET: This article had its headline were updated for clarity.