Boundaries of Russia have changed several times, most recently when Russia annexed part of Ukraine in 2014.
Rationale provided by Russia'sPutin was that many ethnic Russians live in Ukraine.
From the late 1700s onwards, Crimea belonged to Russia/USSR and its eventual inclusion as part of independent state of Ukraine in 1991 was controversial due to large number of ethnic Russians still living there.
2014: a brief period of civil conflict in Crimea ended with territory being annexed by Russia. International community condemned this but no actual steps were taken to prevent it.
In 2015, Russian military intervention began in eastern Ukraine (Donbas region) which has continued ever since.
The Donbas is home to a significant proportion of Ukrainian industry and population, including major cities such as Kharkiv and Dnipro.
Eastern Ukraine is also where the majority of ethnic Russians reside within Ukraine.
The Donbas is home to around 3 million people who are mostly ethnically Ukrainian or Russian speakers.
Since 2014, over 3 million people have been displaced from their homes in Eastern Ukraine.
There is also ongoing violence along the border between Russia and Georgia, particularly in Abkhazia and South Ossetia.
Since 2014, over 6000 civilians have been killed in fighting between pro-Russian separatists and Ukrainian forces.
Displacement has led to increased poverty levels across Ukraine due to loss of income and assets.
Over 70% of those displaced are women and children.
Historical Tensions - The relationship between Ukraine and Russia dates back centuries, with both countries sharing a complex history marked by periods of cooperation and conflict.