Sergey Vasiliev grew up idolizing his older brother. Alexander was the serious one, the better student, but fun-loving Sergey followed him everywhere, hanging out with his friends and treating his every word like the gospel truth.

The two also remained close as adults, even after Sergey left the Black Sea port of more than a million and moved 500 kilometres north to Kiev to start a construction business and be with his girlfriend. Then, four months ago, Ukraine's political turbulence suddenly drove them apart. They reacted very differently to the pro-Western revolution in the capital's Independence Square – the "Maidan."

Sergey, furious at government corruption, charged to the front line in January, clashing with the infamous Berkut riot police. The solution to Ukraine's problems, he had come to believe, lay in ripping up its Soviet foundation and lingering deference to Russia, and building something new, more European in their place.

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This was anathema to all that Alexander, by then a prominent pro-Russian figure, held dear. When the uprising his brother had embraced succeeded, he began to agitate for a counter-revolution.

Three weeks ago, 46 people died here in a fiery partisan clash, but by then Alexander was gone. He had come under police scrutiny as a "separatist," and in March moved with his young family to Crimea. When President Vladimir Putin announced that the peninsula had been annexed to the Russian Federation, he was delighted.

Now, the brothers live on different sides of Europe's new Cold War – and a burgeoning conflict in Ukraine that Russian President Vladimir Putin declared a "civil war" on Friday.

The political divide is often portrayed as splitting the country along linguistic and cultural lines, pitting the Ukrainian-speaking and heavily Catholic centre and west against the Russian-speaking and Orthodox south and east.

That is how the Kremlin and its allies want the fight to be seen. But the real cause of Ukraine's unrest is the one driving the Vasiliev family apart.

On Sunday, a much-anticipated presidential election will show just how sharply divided this country, which once had a population of 45 million, has become. Turnout is expected to be high in the centre and the west, where many are anxious to replace the interim government that has ruled since the uprising with a president who can stitch up the nation's many wounds.

But voting will prove dangerous if not impossible in Donetsk and Lugansk, eastern provinces where government buildings are under the control of pro-Russian separatists. And this time the only Crimeans who will cast ballots are the ones who have fled to escape Russian rule.

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Ukrainian-speakers know how they want the country to proceed, but there isn't nearly as much unity among the country's many Russian-speakers. In many ways, the violence in the south and east is less an inter-communal conflict than an intra-communal one, splitting the Russian-speaking population in two and turning families and friends against each other.

The tale of the Vasiliev brothers could have been torn from the pages of Taras Bulba, the famous Nikolai Gogol short story about two Ukrainian brothers who wind up on opposite sides of a 16th-century war against occupying Poland.

But if Taras Bulba told the tale of the early struggle for an independent Ukraine, the rift between the Vasilievs illustrates how split Russian-speakers are on whether, and how, they belong in an independent Ukraine.

"The main reason for our disagreement is that I think of myself as a proud Ukrainian. My brother thinks of himself as Russian because we are ethnically Russian, and Odessa has always been a Russian city," says Sergey, 32, now married with an 11-year-old adopted daughter.

In an e-mail written from his new home in Sevastopol, the home port of Russia's Black Sea fleet, Alexander, 35, insists that Ukraine is now in a "full-force" civil war. He despairs of ever again being able to visit his beloved Odessa, and worries that his brother and parents will find it difficult to come to Crimea as tensions in Ukraine turn more and more acrimonious.

The threat of violence is constant – two days ago, 13 Ukrainian soldiers were gunned down in a battle with pro-Russian militants near the Donetsk town of Volnovakha.

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But that was far from the bloodiest day since the uprising ended in February.

Odessa's trial by fire

The charred husk of the Trade Union building in the centre of Odessa stands as a ghostly monument to how dangerous and deadly this country's divisions have become.

The five-storey Soviet-era structure overlooks Kulikovo Field, a paved plaza where a small pro-Russian protest camp sprang up as soon as President Viktor Yanukovych's government was toppled.

Other than the few hundred pro-Russians there, and occasional pro-Maidan gatherings at the top of this city's famous Potemkin stairs, Odessa remained quiet throughout the upheaval in Kiev. Tensions grew, however, as neighbouring Crimea declared its independence and then was quickly annexed by Russia.

Like Crimea, the port founded in 1794 by Catherine the Great to be the southern gateway to her empire retained strong cultural ties to Russia after the Soviet Union fell. Some in the city believed passionately, and still do, that Odessa also must return to Mother Russia some day.

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On May 2, a sporting event lit the fuse. Soccer here, as in other parts of Europe, often leads to violence. Fans brawl frequently, and the "Ultras" – truly hard-core supporters – are known both for their rabid devotion and for being Ukrainian nationalists.

But this time the Ultras for Odessa Chernomoretz and visiting Kharkiv Metallist decided that, rather than fight, they would join forces and stage a Ukrainian unity march through the centre of the city. En route, they were attacked by Russian supporters, some armed with guns, and an Odessa Ultra was shot and killed.

Outraged, the Ultras battled back, joined by veterans of the "self-defence forces" who had fought on Maidan against Mr. Yanukovych. Forced to flee, the pro-Russians retreated to Kulikovo Field and regrouped.

Konstantin Ivanov, a 34-year-old businessman and self-defence veteran (shot four times during the battle for Kiev, he is alive only because of a bulletproof vest), says he wanted the conflict to end there. Although ethnic Russian himself, he despised those on the field, but thought clearing their camp was a job for the police.

However, the police were mostly bystanders that day, and the soccer fans, having lost one of their own, were "very aggressive," Mr. Ivanov says. "It wasn't possible to stop the Ultras."

Rather than desert their allies, Mr. Ivanov and the Maidan forces marched with them to Kulikovo, where the pro-Russians quickly disappeared into the Trade Union building. Mr. Ivanov believes this was planned, since people were already on the roof, shooting fireworks down on the crowd. Molotov cocktails were next, thrown by both sides. Soon the building was ablaze, and it was clear that lives were at stake.

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But hatred ruled. As people leaped from windows, some suffering from smoke inhalation, others unconscious and badly wounded from the fall, the crowd set on them. Of the 46 who died that day, 32 were victims of the inferno.

Mr. Ivanov is sympathetic, to a point. "I'm sad for esthetic reasons – it doesn't look good to beat people suffering from inhalation and had jumped out of a building with second– and third-degree burns. They were not dangerous to us," he says.

"But from an ethical position, I think the Ultras had the right to do it. This wasn't a duel. There were no rules, no gentlemen's agreement between the parties. It began with them attacking us with automatic weapons."

Russian state television described the tragedy as "genocide" launched by ethnic Ukrainians. However, in videos on YouTube both sides can be heard screaming at each other and the inert police – in Russian. The battle of Odessa was a fratricidal conflict, the city's Russian-speakers shooting, beating and burning each other, everyone convinced they were doing battle with dangerous stooges manipulated by foreign powers.

"I knew people on both sides," says Sergey, who had come from Kiev to attend the game. Despite his passionate pro-Ukrainian stance, he was too aghast at what he was seeing to join the fracas. Friends were fighting friends, and he knew two of the pro-Russians who died, one in the street fight and the other in the fire.

"What happened in Odessa was very, very sad, and I'm still very, very sad, because I think this will not stop," he says. "It's a civil war now because there are people on both sides who lost their relatives, and they will seek vengeance."

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One people or two?

Ukraine's Russian population arrived in waves, and its history is both complicated and politicized. At one time, Russians and Ukrainians (as well as Belarusians) were considered almost indistinguishable, all rooted in the Kievan Rus, a federation of Slavic tribes that converted to Orthodox Christianity in the 10th century. They emerged as separate entities only in the 13th century after the arrival of the Mongols' "golden horde," which conquered Moscow while much of western Ukraine fell to Poland and Lithuania.

Ukrainian historians emphasize the cultural and religious differences that emerged from that point, and describe periods when the country was part of the Russian Empire and later the Soviet Union as prolonged occupations.

Some Russian historians, however, emphasize the ethnic similarity of the people and portray the independent nations that emerged from the Soviet collapse as unnatural. Many Russians still refer to Kiev as the "mother city" of them and their culture.

Stamping out Ukrainian nationalism was an obsession both for the czars and Soviet rulers . One tactic – a ban on teaching Ukrainian – was so successful that even now Russian is the dominant language in much of Kiev's public life. (Although allowed under Soviet rule, Ukrainian-language schools flourished only in the west. The 1989 census showed that 100 per cent of Crimean students were being taught in Russian.)

The "Russification" effort also saw ethnic Russians encouraged to settle in Ukraine. They moved in to repopulate farmlands abandoned after the Stalin-engineered Holodomor, or Great Famine, of the 1930s, doing the same in Crimea after the 1944 expulsion of its ethnic Tatar population. Jobs in the sensitive defence-industry factories of eastern Ukraine were – in effect, if not by official writ – reserved for ethnic Russians.

By the time of the Soviet collapse in 1991, just under a quarter of the country's population was ethnic Russian, and more than 40 per cent of citizens identified themselves as Russian-speakers – numbers that have declined only slightly since then.

Shortly after Ukraine declared its independence in December, 1991, Crimea – which had been part of Soviet Ukraine only since a 1954 decree by Nikita Khrushchev – voted to join the Russian Federation, but the new government in Moscow was too preoccupied to respond.

Regional-autonomy movements soon sprang up in the south and east, but became a threat to national unity only after the 2004 Orange Revolution, when Mr. Yanukovych was ousted (for the first time) over election fraud and pro-Western Viktor Yushchenko swept to power with support largely from western and central Ukraine.

Alexander Vasiliev says that was when he got involved in politics, joining a pro-Russian party called Motherland. To him, and much of Russified Ukraine, the revolution was a Western-sponsored coup, with Russian-speakers fearing they would somehow be made to speak Ukrainian. It's a narrative that Crimeans clung to in March as they voted to join Russia, and one repeated by the masked gunmen on the barricades in the self-declared Donetsk People's Republic.

Brother Sergey calls the Orange Revolution a "global divorce" – the moment Russia and the West stopped trying to work together, and returned to something like Cold War footing.

In any event, Ukraine has spent the past decade refighting that battle. When Mr. Yushchenko's "orange" coalition fell apart, Mr. Yanukovych improbably returned to power in 2010, this time winning a vote that international monitors called "an impressive display of democratic elections." He swept eastern and southern Ukraine, taking 74 per cent of the vote in Odessa, and – ominously – even higher shares in Crimea, Donetsk and Lugansk.

But last year, despite the political support he received from Moscow, Mr. Yanukovych toyed with signing a trade deal that could have led the country to become a member of the European Union. It was likely a political feint – he risked losing both his alliance with the Kremlin and his base at home – but when Mr. Yanukovych abruptly reversed course in November in favour of closer ties with Russia, he rekindled the political war in earnest.

This time, however, the two sides were far angrier and, rather than seeking a fair election, the Maidan protesters wanted to throw out a fairly elected leader with a year remaining in his mandate. The civil-society groups who had led the Orange Revolution were joined by fringe nationalists, including Right Sector – the ideological descendants of the Ukrainian Patriotic Army, a group led by the legendary and controversial Stepan Bandera that fought both the Nazis and the Soviets in an early bid for independence. They weren't demanding a recount, they wanted to live in a very different country.

Sergey's first taste of combat came late in January during the "Hrushevskoho street riots," when 200,000 pro-Europe demonstrators marched through central Kiev in defiance of new "anti-protest" laws that effectively criminalized the rolling protests on Independence Square. They used clubs and Molotov cocktails on police, who battled back with truncheons, tear gas and, in several instances, live ammunition.

Thin but muscular, he smiles shyly when asked just what took place. "I played an active role. I don't want to say more than that." Four people were killed – three of them shot by police snipers – and the Maidan had its first martyrs. It was the point of no return and, like Odessa later on, the rules had evaporated. There was no more room for compromise.

By chance, both brothers were in Odessa at the end of February when Mr. Yanukovych ordered his riot police to use all means to end the uprising on the Maidan, provoking a furious gun battle that left 100 people dead, nearly all of them protesters. But those defending the square held their ground and – after an EU-brokered peace deal fell apart – the President was forced to flee.

Sergey watched the battle on television with his heart in his throat. He wanted to be there, and says only his brother kept him from heading straight to Kiev. Alexander's suspicions increased the next day, when parliament – anxious to please the angry crowds still on the streets – moved to repeal a Yanukovych-era law that allowed regional governments to adopt Russian as a second official language.

Interim President Oleksandr Turchynov refused to sign the new bill, but it was still a propaganda gift to the Kremlin – proof to Russian-speakers in Odessa, Kharkiv, Donetsk and Lugansk of the new government's hostility to them and their culture.

With Kiev still reeling from the upheaval, Russia sent soldiers in disguise to Crimea to oversee the controversial referendum on separation and then moved tens of thousands of troops to its border with Ukraine. "The essential issue is how to ensure the legitimate rights and interests of ethnic Russians and Russian speakers," Mr. Putin said, questioning whether the belt from Kharkiv in the northeast to Odessa in the south had ever truly been part of Ukraine.

"I would like to remind you that what was called Novorossiya [New Russia] back in the czarist days … was not part of Ukraine back then," he added in remarks televised across Russia and much of eastern Ukraine. "These territories were given to Ukraine in the 1920s by the Soviet government. Why? Who knows?"

So Mr. Putin deliberately sowed the seeds of the separatism movement now roiling the Donetsk and Lugansk regions. In fact, Alexander Vasiliev was forced to flee Odessa after he too referred to the city as part of "Novorossiya" in a public speech. "I think it is the most appropriate name for these lands," he argues, but asking him and his brother how they feel about the Russian President is perhaps the easiest way to see what sets them apart.

Although he admits to concerns about corruption in Russia and the lack of dissent, Alexander says that "Putin is undoubtedly one of the most influential world leaders today. There's no doubt that under his rule Russia is strengthened, and the standard of living of the majority of citizens has increased significantly."

Mention Mr. Putin to Sergey, however, and he responds only in expletives.

How their parents feel Sunday's election is likely to see Petro Porashenko, a billionaire chocolatier and key financial backer of the Maidan, swept to power ahead of former prime minister Yulia Tymoshenko, another Maidan idol. But Sergey is the only member of his family planning to vote, and even he, in a clear sign of how far Mr. Porashenko must go to win over the Russian-speaking minority. says he'll spoil his ballot by marking "against all."

There is no serious candidate from the south or east who can claim to represent those who backed Mr. Yanukovych in 2010 (he took 49 per cent of the final national vote versus 45 per cent for Ms. Tymoshenko). For many Russian-speakers, the election is simply to decide which tycoon who supported the Maidan (Ms. Tymoshenko is also believed to be a billionaire) will reap the rewards.

Also unwilling to exercise their franchise, the Vasiliev brothers' parents fear that Ukraine's swirling politics may have broken up their once-close family forever. Their granddaughter, Alexander's 3-year-old Sofiya, now lives on the other side of a de facto international border, and it isn't clear if, when or where they will be able to see her again.

"It's sad," says Natalya Vasilieva, 60, a former oceanographer, sniffling as she shuffles photographs of her family.

"We don't know when Alexander will be able to come back. It's not safe for him and his family in Odessa."

She and her 57-year-old husband – also named Alexander – have retired to a village outside Kherson, a city 200 kilometres east of Odessa, where they live on her pension while he tends a hobby vineyard. Like many older Russian-speakers, they share their first-born son's pro-Putin views and pine for the stable life they say they had before the Soviet breakup.

They consider the rise of a government with ties to Right Sector an insult to their own parents, who fought in the Soviet army when it "liberated" Ukraine from the Nazis. There are statues to Stepan Bandera in Western Ukraine, but on the outskirts of Kherson, calling people "Banderites" is the same as calling them the enemy.

Their younger son's front-line role during the revolution leaves them confused and angry.

"I was very upset when I found out Sergey was involved in the events at Hrushevskoho Street," his father says, staring at the kitchen table.

"He was never in the army. He doesn't understand what it means to take an oath. He was fighting against guys in the police who were upholding their oaths. An oath is a sacred thing."

Mr. Vasiliev says his is not the only family divided by the conflict – some have "much bigger divisions: People are getting divorced."

His sons recoil at the idea of taking up arms against each other, as the brothers in Taras Bulba did, insisting they have decided to stop discussing politics with each other and will always put family above all else.

But Alexander says he could see himself taking part in the "insurrectionary movement" in eastern and southern Ukraine, while Sergey vows to do his duty if the army ever calls up men his age to fight for their country.

Why are the brothers so diametrically opposed? Their parents think it's because of their slight difference in age.

Alexander was born in 1979, Sergey in 1982. "The two boys are only three years apart, but they belong to different generations," their mother explains. "They were in their youth when they lived through a turning point in history."

Because he was 12 when the Soviet Union fell, Alexander was old enough to be angry when told he suddenly lived in another country. "If someone came to your country and changes its name, would you stop loving your motherland?" Natalya asks.

Sergey, however, was just 9 and "didn't feel that loss – he doesn't remember the transition," she adds.

"For him, Ukraine is his motherland."