Why is Russia invading Ukraine and what does Putin want?

These are terrifying times for the people of Ukraine and horrifying for the rest of the continent, witnessing a major power invading a European neighbour for the first time since World War Two.

Dozens have died already in what Germany has dubbed “Putin’s war”, both civilians and soldiers. And for Europe’s leaders, this invasion has brought some of the darkest hours since the 1940s.

It was, said France’s Emmanuel Macron, a turning point in Europe’s history. Recalling the Cold War days of the Soviet Union, Volodymyr Zelensky spoke of Ukraine’s bid to avoid a new iron curtain closing Russia off from the civilised world.

For the families of both armed forces, there will be anxious days ahead. Ukrainians have already suffered a gruelling eight-year war with Russian proxies. The military has called up all reservists aged 18 to 60 years old.

Top US military official Mark Milley said the scale of Russian forces would mean a “horrific” scenario, with conflict in dense urban areas.

This is not a war that Russia’s population was prepared for, either, as the invasion was rubber-stamped by a largely unrepresentative upper house of parliament.

The invasion has knock-on effects for many other countries bordering both Russia and Ukraine. Five countries are seeing an influx of refugees, while the UN children’s agency says its projected scenario is for up to five million refugees. Poland, Moldova, Romania, Slovakia and Hungary are all braced for arrivals.

Nato has put warplanes on alert, but the Western alliance has made clear there are no plans to send combat troops to Ukraine itself. Instead, they have offered advisers, weapons and field hospitals.

Meanwhile, 5,000 Nato troops have been deployed in the Baltic states and Poland. Another 4,000 could be sent to Romania, Bulgaria, Hungary and Slovakia.

At the same time, the West is targeting Russia’s economy, financial institutions and individuals:

Ukraine has urged its allies to stop buying Russian oil and gas. The three Baltic states have called on the whole international community to disconnect Russia’s banking system from the international Swift payment system. That could badly affect the US and European economies and Germany says is reluctant to agree to it.

The Russian city of St Petersburg will no longer be able to host this year’s Champions League final for security reasons.

President Putin partly blamed his decision to attack on Nato’s eastward expansion. He earlier complained Russia had “nowhere further to retreat to – do they think we’ll just sit idly by?”

Ukraine is seeking a clear timeline to join Nato and Russia’s Deputy Foreign Minister Sergei Ryabkov explained: “For us it’s absolutely mandatory to ensure Ukraine never, ever becomes a member of Nato.”

Last year, President Putin wrote a long piece describing Russians and Ukrainians as “one nation”, and he has described the collapse of the Soviet Union in December 1991 as the “disintegration of historical Russia”.

He has claimed modern Ukraine was entirely created by communist Russia and is now a puppet state, controlled by the West.

President Putin has also argued that if Ukraine joined Nato, the alliance might try to recapture Crimea.

But Russia is not just focused on Ukraine. It demands that Nato return to its pre-1997 borders.

Mr Putin wants Nato to remove its forces and military infrastructure from member states that joined the alliance from 1997 and not to deploy “strike weapons near Russia’s borders”. That means Central Europe, Eastern Europe and the Baltics.

In President Putin’s eyes, the West promised back in 1990 that Nato would expand “not an inch to the east”, but did so anyway.

That was before the collapse of the Soviet Union, however, so the promise made to then Soviet President Mikhail Gorbachev only referred to East Germany in the context of a reunified Germany. Mr Gorbachev said later “the topic of Nato expansion was never discussed” at the time.

Nato is a defensive alliance with an open-door policy to new members, and its 30 member states are adamant that will not change.

There is no prospect of Ukraine joining for a long time, as Germany’s chancellor has made clear.

But the idea that any current Nato country would give up its membership is a non-starter.

Not for now. Ukraine has called for talks, but Russia says they can only be held on condition that Kyiv agrees to surrender and demilitarise, and that will not happen.

As well as the war, any eventual deal will need to involve with the West in the east and arms control.

The US had offered to start talks on limiting short- and medium-range missiles, as well as on a new treaty on intercontinental missiles. Russia wanted all US nuclear arms barred from beyond their national territories.

Russia had been positive towards a proposed “transparency mechanism” of mutual checks on missile bases – two in Russia, and two in Romania and Poland.