Russian troops have entered two regions of Ukraine on what the Kremlin describes as a “peacekeeping operation”.

In response, Western nations including the US and the UK have announced economic sanctions on Russia.

So how did we get here? And what consequences could Russia face?

How did we get here?

Russia has amassed an estimated 150,000 troops around the borders of its neighbour, and former member of the USSR, Ukraine.

This has led Western governments and media to express concern over a possible Russian invasion in recent months.

Though it’s more accurate to say that the fear is of another invasion. Russia has already invaded, and continues to occupy, part of Ukraine: the Crimea peninsula. Understanding what happened there is key to understanding the current crisis.

Like many areas that border Russia, Crimea has a significant Russian-speaking population and there are some in the region who would like it to break away from Ukraine and become part of the Russian Federation.

Those pro-Russian separatists had their moment in 2014, when the Ukrainian president was ousted in a national revolution and Russia sent its troops into Crimea.

A few weeks later, Crimea declared itself independent from Ukraine following a referendum, which appeared to show huge support for joining Russia.

But a United Nations (UN) resolution said the referendum had “no validity” because Russian troops had already entered Crimea at the time ballots were cast and because the vote had not been authorised by the Ukrainian government.

The results themselves – which the separatists claimed were based on a huge turnout – were also called into question as ethnic Ukrainians and members of the Tatar community said they’d boycotted the vote.

Nevertheless, after the referendum, the Kremlin announced that Crimea had become part of Russia.

The majority UN members disagreed and continue to recognise Crimea as part of Ukraine. Russian troops still occupy the region.

What’s happening now?

The latest crisis involves two other parts of Ukraine, Donetsk and Luhansk, which are sometimes referred to collectively as the Donbass.

Both areas border Russia and, like Crimea, held disputed referendums in 2014 on whether to leave Ukraine and join their larger neighbour.

Russia was less enthusiastic in its response to these ballots, and unlike in Crimea, it declined to recognise the regions as independent from Ukraine. Nevertheless, the Kremlin said the pro-independence results should be implemented.

Since then, Ukrainian forces and pro-Russian separatists have been at war in the area, with dozens of shaky ceasefires agreed (and broken by both sides) over that time.

Moscow is widely accused of giving the rebels military assistance. Pro-Russian forces shot down Malaysian Airlines flight MH17 in July 2014 with a missile launcher supplied by the Russian army, according to a Dutch-led investigation, though Russia denies any involvement.

More than 13,000 people have died in the Donbass conflict, including over 3,000 civilians, in what’s been dubbed Europe’s “forgotten war”.

In this context, Vladimir Putin’s decision on Monday to recognise Donetsk and Luhansk as “people’s republics” independent of Ukraine is considered very significant.

He claims that Russian-speaking civilians in the two regions are experiencing a “genocide” at the hands of Ukrainian forces.

The US says Russia is trying to give itself an excuse to invade.

We can’t see inside the mind of President Putin, but in a speech he gave last night he was clear that he sees Ukraine as “not just a neighbouring country” but as “an integral part of [Russia’s] own history, culture, spiritual space”.

Today, the Russian foreign minister Sergei Lavrov questioned whether Ukraine had a right to sovereignty, according to reports from the Russian news agency Interfax.

And Russia’s recent actions certainly have parallels to the invasion of Crimea nearly a decade earlier.

By recognising the two Donbass regions as independent of Ukraine, and claiming that there are human-rights violations underway there, the Russian president seems to think he can make the case for moving his forces into Donetsk and Luhansk.

And that’s what he’s now done.

The Kremlin says the troops are there on “peacekeeping duties”, a claim that’s been met with scepticism in the West. The US ambassador to the UN said last night: “We know what they really are.”

What consequences could Russia face?

Russia is already experiencing economic sanctions – where other countries impose financial measures or constraints designed to damage another nation’s economy – as a result of its actions this week.

Within hours of Russia’s decision to recognise Donetsk and Luhansk as independent republics, the White House said it would ban US citizens from doing business in the regions.

And the Biden administration says it will implement further “swift and severe economic measures” if Russian troops go beyond Donbass and attempt to invade the rest of Ukraine.

Meanwhile Boris Johnson said today that the UK assets of five Russian banks and three wealthy Russian individuals would be frozen – meaning their owners cannot move or access them.

The prime minister said it was “the first tranche […] of what we are prepared to do”.

And perhaps the most significant challenge for Russia so far is Germany’s decision to block the certification of the Nord Stream 2 pipeline, which would take gas from northern Russia into Germany.

Selling natural gas to Europe is a vital part of Russia’s economy, so the loss of this pipeline – which would have doubled its supply capacity on the continent – is expected to hit the country hard.

Less than 5 per cent of Britain’s gas comes from Russia, but for the EU, the figure is closer to 50 per cent – so Germany’s decision will have knock-on effects for Russia’s customers in the West too.

Those are just some of the economic implications of Russia’s moves in Ukraine this week. But what about a military response from Western countries? Could we end up at war with Russia?

It’s worth remembering that Ukraine is not a member of NATO, the military alliance that includes many European states and the US.

That’s key because NATO rules say that an attack on one NATO member is an attack on all. If Ukraine had been part of the bloc, Russia’s invasion of Crimea in 2014 and the Donbass this week would have meant it risked war with all 30 NATO states.

But while it’s not a NATO member, Ukraine has strengthened its links with the West in recent years. In 2020, NATO officially recognised it as an “Enhanced Opportunities Partner” and since Russia’s 2014 invasion of Crimea, the constitution of Ukraine has explicitly named joining NATO as a priority.

Nevertheless, while Western nations have been clear that they support Ukraine in the face of Russian aggression, NATO members including the UK have said they would not send troops in the event of an invasion.

We updated this article on 26 February 2022 to clarify that an attack on a NATO member could risk war with the alliance, rather than automatically triggering it.