Russo-Turkish War: The Russian Empire declares war on the Ottoman Empire.

The Russo-Turkish War (1877–1878) was a conflict between the Ottoman Empire and a coalition led by the Russian Empire which included Romania, Serbia, and Montenegro. Precipitating factors included the Russian goals of recovering territorial losses endured during the Crimean War of 1853–1856, re-establishing itself in the Black Sea and supporting the political movement attempting to free Balkan nations from the Ottoman Empire. The Romanian army had around 114,000 soldiers in the war. In Romania the war is called the Russo-Romanian-Turkish War (1877–1878) or the Romanian War of Independence (1877–1878).

The Russian Empire was an empire that spanned most of northern Eurasia from its establishment in November 1721 until the proclamation of the Russian Republic in September 1917. At its height in the late 19th century, it covered about 22,800,000 km² (8,800,000 sq mi), roughly one-sixth of the world's landmass, making it the third-largest empire in history, behind only the British and Mongol empires. It also colonized Alaska between 1799 and 1867. The empire's 1897 census, the only one it conducted, found a population of 125.6 million with considerable ethnic, linguistic, religious, and socioeconomic diversity.

The Ottoman Empire, also called the Turkish Empire, was an imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Central Europe, between the early 16th and early 18th centuries.