So, what is at the heart of the conflict that has been going on for more than seven years?
Russia on Thursday attacked Ukraine, with the sound of explosions on the edge of Ukraine’s capital and air sirens prompting the city residents to panic and flee for safety.
But how did it get to this stage?
US earlier warned that Russia had amassed more than 100,000 Russian soldiers on the border with Ukraine and in annexed Crimea in recent weeks.
This has stoked fears in Kyiv and the West that the Kremlin may start a new war with its neighbour and former province that chose to break away from Moscow’s political orbit, Al Jazeera reports.
Earlier this month, a top Ukrainian military expert told Al Jazeera that Russia could invade Ukraine as early as January, unleashing a “brief and victorious” war.
But Russia denies it is planning an invasion. Moscow says it can move Russian troops wherever it wants and that any of its acts are defensive. Russian officials, including President Vladimir Putin, have for their part warned NATO against expanding eastwards.
So, what is at the heart of the conflict that has been going on for more than seven years?
What is now Ukraine, Russia and neighbouring Belarus were born on the banks of the Dnieper River, almost 1,200 years ago in Kievan Rus, a medieval superpower that included a huge chunk of Eastern Europe.
But Russians and Ukrainians parted ways linguistically, historically and, most importantly, politically.
Putin has, however, claimed repeatedly that Russians and Ukrainians are “one people”, part of the “Russian civilisation” that also includes neighbouring Belarus. Ukrainians reject his claims.
Ukraine went through two revolutions in 2005 and 2014, both times rejecting Russia’s supremacy and seeking a path to join the European Union and NATO.
Putin is particularly enraged by the prospect of NATO bases next to his borders and says Ukraine joining the US-led transatlantic alliance would mark the crossing of a red line.
Backing the rebels
After Ukraine’s 2014 Revolution of Dignity, which saw months-long protests ultimately topple pro-Moscow Ukrainian president Viktor Yanukovych, Putin used the power vacuum to annex Crimea and back separatists in the southeastern provinces of Donetsk and Luhansk.
The rebels carved out two authoritarian, economically weak “People’s Republics”, where the death penalty was restored. They ran dozens of concentration camps where dissidents were tortured and executed.
Professor Ihor Kozlovsky of the Donetsk State University spent almost 700 days in the concentration camps and prisons, and says he was tortured by separatists and Russian officers who retold him Putin’s claims about the “Russian civilisation”.
“The officer told me, ‘There are no nations, there are civilisations, and the Russian world is a civilisation, and for anyone who had been part of it, it does not matter what you call it, a Tatar or a Ukrainian, you don’t exist,’” he told Al Jazeera.
The war – and the way the separatists abuse their opponents and mismanage their “republics’” economies, cooled pro-Russian sentiment in Ukraine.
“Paradoxically, Russia is helping to strengthen the Ukrainian sense of nation that some Russian politicians claim does not truly exist,” Ivar Dale, a senior policy adviser with the Norwegian Helsinki Committee, a rights watchdog, told Al Jazeera.
The conflict turned into Europe’s hottest war. It has killed more than 13,000 and displaced millions.
In 2014, the Ukrainian military was under-equipped and demoralised, while the rebels had Russian “consultants” and weaponry.
However, these days, Ukrainians are much stronger militarily and morally, and thousands of volunteers who helped repel the separatists are ready to do it again.
Ukraine bought or received advanced weaponry from the West and Turkey, including Javelin missiles that proved lethal to separatist tanks, and Bayraktar drones that played a crucial role in last year’s war between Azerbaijan and Armenia.
Former US President Donald Trump’s first impeachment was triggered by his suspension of military aid and arms exports to Kyiv.
Meanwhile, Ukraine has boosted domestic development and the production of arms – some of which are just as effective as Western weaponry.
An economic dimension
Apart from ideological and political reasons, Putin had desperately sought Ukraine’s membership in a Moscow-dominated free-trade bloc which launched in 2000.
The Eurasian Economic Community (EAEC) united several ex-Soviet republics and was widely seen as a first step to reincarnate the USSR.
With a population of 43 million and a powerful agricultural and industrial output, Ukraine was supposed to be the most essential part of the EAEC after Russia, but Kyiv refused to join.
“To create a self-sufficient market, one needs a population of about 250 million,” Aleksey Kushch, a Kyiv-based analyst, told Al Jazeera, referring to theories by Nobel-prize winning economist Paul Krugman.
“Krugman’s models are a basis for the bloc’s architectonics, and for the union [to work], Ukraine and Uzbekistan [with a population of 34 million] need to be included. That’s why there are permanent geo-political wars around these nations,” Kushch said.
Ukraine’s economy sank after severing ties with Russia, its one-time largest economic partner.
But seven years into the conflict, the recession is over, as world prices for grain and steel, Ukraine’s main exports, skyrocket, and as Ukrainian companies and labor migrants find new ways to the West.
Why now?
Putin’s approval ratings are going down as Russians resist vaccinations and decry the economic hardships brought on by the pandemic.
The Kremlin remembers his stratospheric ratings of almost 90 percent after Crimea’s annexation, and a new war or escalation may distract the public from domestic problems and boost Putin’s popularity.
He also seeks to restore dialogue with the West, especially the US, and amassing an army next to Ukraine has worked already.
In the spring, tens of thousands of troops were deployed next to Ukraine – and in June, Putin got his first face-to-face meeting with US President Joe Biden.
The presidents held a two-hour video conference on December 7, and Biden threatened Putin with tougher economic sanctions and a reposition of NATO troops in Europe.
But Putin still wants to see him in person.
“We will definitely meet, I would really like that,” he told Biden, according to a video released by Russian media on Tuesday.