The high casualty rates of the Crimean and Russo-Turkish Wars made Russia realise it needed to modernise, throughout the 19th century, reforms took place, serfdom was abolished, and the army was modernised, when Nicholas ll came to the throne in 1894, he married Princess Helene of Orleans, cementing Russia's alliance with France.
In 1905 Japan declared war on Russia, it had been fighting a weak Chinese Republic, and controlled Peking, most of the coastline and Manchuria, since the Qing dynasty was deposed by the Great Powers in the aftermath of the Boxer Rebellion. Japan made peace with China to concentrate on Russia, Japan overran Sakhalin, which was barely defended and besieged Port Arthur, which turned out to be a massive drain on resources.
Brusilov was made a General, and given the task of retaking Sakhalin. Japan requested that its ally Thailand join the war, and the Russian Baltic Fleet was sent from St Petersburg to join the fight.
Brusilov repels an attack on the Southern Kurils and, using the fleet attached to his army lands on northern Sakhalin, where Russian settlers greet him after fighting a guerrilla campaign against the Japanese. On the diplomatic front, Thailand declines to declare war, while Montenegro, Romania and Serbia declared war on Japan, and Montenegro pledged to sent troops.
On Sakhalin, the Japanese supply lines cut by Russian Partisans, Brusilov easily defeats isolated Japanese forces. China is on the verge of declaring war on Japan, so Japan instigates successful revolts in Tibet and Mongolia to distract China. The Dalai Lama returns from Sikkim to rule Tibet, and Mongolia becomes The Khanate of Mongolia and Namjil Wangchuk, a descendant of Ghenghis Khan, is named Khan of Mongolia.
Russia gives Tuva to Mongolia, and Mongolia allies to Russia against Japan, Mongolians raid Japanese outposts in Manchuria. The Baltic Fleet arrives at Tsushima, and defeats a small fleet of ships, the bulk of the Japanese fleet sails to Port Arthur in one huge effort to take the city, when the Russian fleet reached Port Arthur, they engaged the Japanese, in 45 minutes the Japanese fleet was decimated, General Maresuke Nogi gave his surrender to Oskar Victorovitch Stark, the Russian admiral.