The war has killed thousands of civilians, forced over a third of Ukraine's 41 million people from their homes, left cities in ruins and shaken global markets. It is largely at a standstill with no immediate prospect of peace talks.
In addition to Crimea, which Russia annexed in 2014, Russian forces have expanded control to areas of the south including the Black Sea and Sea of Azov coasts, and chunks of the eastern Donbas region comprising the provinces of Luhansk and Donetsk.
Ukraine's armed forces have said almost 9,000 military personnel have been killed in the war.
Russia has not publicised its losses but U.S. intelligence estimates 15,000 killed in what Moscow calls a "special military operation" to "denazify" Ukraine. Kyiv says the invasion is an unprovoked act of imperial aggression.