Explained: What prompted Putin's invasion of Ukraine, Russia's global defiance

Russia launched a 'military operation' against Ukraine - effectively an invasion - early Thursday morning, triggering global fears of a major multi-national armed conflict. Russian President Vladimir Putin announced the attack in a televised address, which follows his declaration that a 2015 peace deal agreed to stop fighting over breakaway regions of Donetsk and Luhansk - is invalid.

What followed was reports of explosions and missile strikes at key Ukraine cities, including capital Kyiv and in rebel areas of Donetsk and Luhansk. 

Ukraine President Volodymyr Zelenksy has claimed Russia had massed nearly 200,000 troops on his country's borders.

So far, Russia has claimed the destruction of airbases and air defences, while Ukrainian military says it has shot down six Russian aircraft in Luhansk. 

Ukraine has also claimed that it has killed ‘at least 50 Russian occupiers’. Over 40 Ukrainian soldiers and 10 civilians are believed to have also died so far.

Russia's actions have been condemned by almost all major nations, including the United States, the European Union, the United Kingdom, and Canada. UN chief Antonio Guterres has urged Putin to stop the war ‘in the name of humanity’, warning of devastating consequences for Ukraine and the world.

Why has Russia attacked Ukraine?

Russia believes Ukraine is moving closer and closer to the West via both the NATO, or North Atlantic Treaty Alliance, and the European Union. 

Ukraine is not a member of NATO but has cooperated with the alliance and frequently expressed its intention to sign up.

Putin, however, is aware Ukraine joining NATO significantly increases the difficulty of bringing Donetsk and Luhansk within his control. He has also frequently accused Ukraine of being a 'puppet' in the hands of the West.

The removal of pro-Russian Viktor Yanukovych as President of Ukraine - he was voted out by the Ukrainian parliament in February 2014 - triggered Russia's annexation of the strategically valuable Crimea peninsula eight years ago.

A former member of the Soviet Republic - it gained independence only in 1991 - Ukraine still has deep social, historical, cultural, and political ties to Russia, but relations have been strained since 2014.

Fearing it could be surrounded by what it sees as hostile forces if Ukraine joins NATO, or moves any closer to the West, the Kremlin has demanded guarantees NATO will not accept it or other former members of the Soviet Republic. 

Western countries, and NATO, have dismissed such fears, but Putin is clearly not buying their statements.

Russia's defiance in the face of sanctions

The US, the European Union, the UK and other countries have all slapped sanctions on Russia, targeting its banks (to cut funding to operations in rebel regions) and the lawmakers who approved the use of force.

Read: Biden announces new Russia sanctions

Read: Canada imposes sanctions on Russia, says Trudeau

Putin, however, seems unconcerned.

Earlier this week Russian Foreign Minister Sergei Lavrov brushed off the threat of sanctions, saying, "We're used to it. We know that sanctions will be imposed anyway, in any case. With or without reason."

"They are already threatening us with all manner of sanctions or, as they say now, 'the mother of all sanctions'," he said.

Read: What are sanctions and how could Western countries target Russia

Putin is also possibly secure in the knowledge that the US and other western nations will think twice (and maybe thrice) before deploying troops themselves, and risk turning this conflict into a potentially global one.

The threat of a prolonged military operation is something Putin can sustain almost indefinitely, if he is willing to pay the cost of keeping a large number of troops and equipment in the field, according to two retired US military commanders quoted in a report by Bloomberg.

As he launched the ‘military operation’, Putin said: “Whoever tries to interfere with us, and even more so to create threats for our country… Russia's response will lead you to consequences you have never experienced in your history.”

With input from AFP, Bloomberg, Reuters