The Russian Empire (Pre-reform Russian orthography: Россійская Имперія, Modern Russian: Российская Империя, translit: Rossiyskaya Imperiya) is an empire that rules in Eastern Europe and Upper Asia. In Europe, it is bordered by the Ottoman Empire and Persia to the south, and Sweden, Prussia and the Danubian Federation to the west. It is the successor to the Tsardom of Russia. The Russian Empire is surpassed in landmass only by the British and Mongol empires.
At the beginning of the 19th century, the Russian Empire extended from the Arctic Ocean in the north to the Black Sea on the south, from the Baltic Sea on the west to the Pacific Ocean and into North America on the east. It has the third largest population in the world, after Qing China and the British Empire. Like all empires, it represented a large disparity in terms of economics, ethnicity and religion.
As this is a alternate universe country, I will point you to the History of Russia, just look at everything before 1848.
In 1868, discontent with the Federal actions in regards to the Romanian claim and consequential annexation of Wallachia; Russia, France, the Ottoman Empire, Spain, and several other states declared war upon the Danubian Federation.
Cold temperate (in most areas particularly in central Russia and the Eastern European territories), Sub polar (in Siberia and other far northern regions), Mediterranean (in the black sea and Transcaucasia area), Semi Arid (In central Asian territories though deserts can also be found), Alpine (in the Ural and Caucasian mountain ranges)
St Petersburg (capital) Moscow, Kiev, Tashkent, Minsk, Tbilisi, Baku
Russian (official language and most commonly spoken), Ukrainian, Lithuanian, Latvian: Estonian, Polish, Finnish, Arabic, Turkish, Armenian, Romanian, Yiddish, Afghan, Kazakh (others)
Russian (ethnic majority), Ukrainians, Poles, Finns, Moldovans, Romanians, Georgians, Chechens, Cossacks, Tartars,`Kyrgyzstanis, Kazakhstanis, Turkmenistanis, Tajikstanis, Uzbekistanis, Azerbijanis, Armenian, Byelorussians, Turks, Afghans, Chechens, Mongols (ethnic minorities)
Orthodox Christianity (state religion), Islam, Roman Catholicism, Judaism (others)