Russian invasion of Manchuria

Background
The Russian Empire long had designs on Manchuria as part of their Imperialist expansion across Eurasia. In the aftermath of the First Sino-Japanese War, Russia was alarmed at the rate in which Japan occupied Manchuria and achieved victory, leading the Russians to speed up their designs on Manchuria.

With the building of the South Manchurian Railway, Mukden became a Russian stronghold, which occupied it after the Boxer Rebellion. As with all other major powers in China, Russia demanded concessions along with the railroad.

During the outbreak of the Boxer Rebellion Russia became involved due to its presence in the legations. Russian Cossacks participated in the Eight Nation Alliance relief forces during the Seymour and Gaselee expeditions, and Russian forces were present inside the legations during the sieges in Beijing and Tianjin. These forces were separate from the invasion of Manchuria, with the entire invasion exclusively directed by Russians.

Campaign
The conflict was entirely bilateral, between Qing and Russian forces only.

The Chinese forces in Manchuria were composed of the ethnic Manchu Eight Banners, and Han Chinese Boxers.

Manchuria was also swarming with Han Chinese Honghuzi bandits, since the Qing rulers exiled Chinese criminals to Manchuria as a punishment. Chuang Guandong

Edicts were posted by Boxers calling for attacks on Russian colonists and railroads in Manchuria. The Boxers attacked the South Manchurian railway and sought to destroy it.

The Chinese treated Russian civilians leniently and allowed them to escape to Russia, even notifying them since a state of war existed, that they should leave the war zone, by contrast, Russian Cossacks killed civilians who tried to flee in the Chinese villages, westerners noted that the Chinese followed "civilized warfare" while the Russians massacred people. The Chinese summoned all available men to fight, and the Chinese forces and garrisons gathered artillery and bombarded Russian troops and towns across the Amur. Despite the Cossacks repulsing Chinese army crossings into Russia, the Chinese army troops increased the amount of artillery and kept up the bombardment. In revenge for the attacks on Chinese villages, Boxer troops burned Russian towns and almost annihilated a Russian force at Tieling. The Russians eventually cleared the river and crossed it for the invasion into Manchuria.

100,000 Russian troops participated in the invasion.

The Russians invaded Manchuria during the rebellion, which was defended by Manchu bannermen. The bannermen were annihilated as they fought to the death against the Russians, each falling one at a time against a five pronged Russian invasion. The Russian historian Sergeĭ Mikhaĭlovich Shirokogorov reported that the Russians killed many of the Manchus, thousands of them fled south. The Cossacks looted their villages and property and then burnt them down. Manchuria was completely occupied after the fierce fighting that occurred.

Aftermath
Sergei Witte advised the Czar to withdraw Russian forces from Manchuria, but Kuropatkin advocated for a continued Russian presence in Manchuria. The Russians tried to secure agreements favorable to themselves in exchange for withdrawal, but China refused.

The Honghuzi continued to plague Manchuria despite multiple attempts aiming for their eradication and mass killings directed at them by Cossack forces. They were enlisted by the Japanese during the Russo-Japanese War to attack the Russians on their rear.

Russo-Japanese War
Japan was angered that Russia had not withdrawn according to the treaty it signed in the Boxer Protocol in which it promised to withdrawal from Manchuria.

The Chinese supported Japan during the war.