The Russo-Japanese war was fought between Japan and Russia in 1904, continuing into early 1905. It ended in a defeat for the Russians.
One problem that Russia faced at the turn of the 20th century was that Russia lacked any warm-sea ports, meaning that all the ports they had were quite often frozen over and only functional at specific times of the year. Prior to the war, from 1897, the Qing dynasty of China leased a port called Port Arthur to the Russians which was functional all year round. However, there were developing tensions between the Japanese and the Russians due to Japan fearing that Russia’s previously exhibited expansionist policy would mean that they would soon try to encroach on Japan’s sphere of influence. Japan tried to offer a compromise in which they would recognise the Manchuria area of China as being under Russian dominance in exchange for Russia recognising that Korea was under Japanese influence. Russia disagreed and instead wanted a neutral buffer zone in Korea above the 39th parallel. Japan responded by attacking the Russian Eastern Fleet at Port Arthur on the 9th of February 1904.
Throughout the war there were some crushing defeats for Russia but, despite this, Nicholas II continued to insist that they would win and continued to fight instead of surrendering, even though Japan offered many armistices and suggested bringing the dispute to the Arbitration Court at the Hague.
The war eventually finished in January 1905, with the official treaty (the Treaty of Portsmouth) being signed and overseen by the US President Roosevelt in September that year.
what was the significance of this defeat?
Internationally, it represented the first time in recent history that and Asian power had defeated a Western/European power in combat. It also was the turning point in which Japan emerged as a great power and it signalled the the international stage that Russia’s power and influence in the Eastern regions was decreasing.
Domestically, the massive loss of life with no victory, combined with the fact that Nicholas had been so sure about winning and then failed, and then with the events of Bloody Sunday, all cumulated in the massive wave of unrest and general disturbance that spread throughout Russia from 1905 to 1907.