What's the history between Russia, Ukraine and the West?

Despite fears that it would happen, the move has caused shock around the world.

The Ukrainian army is fighting against the Russian army and millions of refugees have fled to neighbouring countries, such as Poland.

This action has been heavily criticised by the USA , the UK and groups of countries like the United Nations, the European Union and the military alliance, Nato.

Russia, Ukraine and western countries have a long and complex history. Read on to find out more about the some of their most significant recent events.

1922 - 1991: USSR

Image source, Getty Images

Image caption, This map shows the 15 countries that together made up the USSR, also known as the Soviet Union

Russia and Ukraine both used to be part of a very big country called the Soviet Union, and before that the Russian Empire.

In 1922, the Union of Soviet Socialist Republics (the USSR) - better known as the Soviet Union, was formed.

The USSR was a communist country, with its headquarters in Russia's capital Moscow, and it did not agree with western, capitalist countries (like the UK and the US) and their way of doing things.

The USSR existed until 1991, when it was broken up into 15 smaller countries.

1940s - 1991: Cold War

Image caption, The arrival of these two leaders - US President Ronald Reagan in 1980 and USSR premier Mikhail Gorbachev in 1985 - changed the course of the Cold War

There have also historically been tensions between the West and Russia.

The Cold War was a 40-year division between the Soviet Union and western countries (the US and its allies, like Britain), which started in the 1940s and lasted until 1991.

It was a war between two ideas and ways of ruling - communism in the East and capitalism in the West.

Even though the Cold War came to an end over thirty years ago, Russia and the West still don't always agree with each other.

2014: Crimea

Ukraine shares borders with both European Union countries and Russia - but as an old member of the Soviet Union, it has deep ties with Russia, with many Russians living in the country and Russian being widely spoken there.

Some Ukrainians want the country to have closer ties to the European Union, but others want it to have closer ties to Russia.

In 2014, Russia took back control of an area of Ukraine called Crimea in southern Ukraine.

Ever since then, Ukraine's army has been locked in a war with Russian-backed rebels in eastern areas of Ukraine near the border with Russia.

The conflict has caused at least two million people to flee their homes and 14,000 people have lost their lives.