Feb. 27 has become a dark day for both Ukraine and Russia. A year ago on that day, heavily armed men seized the Crimean parliament, and Russian soldiers fanned out across the peninsula, making its annexation a fait accompli within hours. This year, liberal Russian opposition leader Boris Nemtsov, a fierce critic of the Kremlin’s policy toward Ukraine, was gunned down in cold blood in central Moscow.

Just a day earlier, Russian President Vladimir Putin had signed a decree designating Feb. 27 “Special Forces Day.” The Russian government’s official newspaper explained the choice of date obliquely: “Remember what happened where a year ago, and how it all ended.” Putin, at the time, denied Russian involvement in Crimea, just as today he denies Russian involvement in eastern Ukraine.

Disagreement over Russia’s role in Ukraine — and Ukraine’s role in Russia — has become the most bitter issue dividing Russians today. The vast majority backs Putin’s course: 84 percent of Russians approve of Crimea’s annexation and 62 percent believe eastern Ukraine should become independent or join Russia, according to a poll taken by the independent Levada Center in January. The omnipresent state TV channels have branded the minority supporting Ukraine’s territorial integrity as a traitorous “fifth column.”

Nemtsov, who ran a cottage industry publishing reports on the corruption gnawing away at Russia, was reportedly about to release an investigation into Russian military involvement in eastern Ukraine. He was also one of the organizers of an “anti-crisis” protest march, planned for March 1, demanding fair elections and “the immediate end to the war and any aggressive actions toward Ukraine.” After Nemtsov’s murder, the demonstration was hastily reformatted into a memorial procession attended by tens of thousands of people. Isolated yellow and blue Ukrainian flags could be seen in the sea of red, blue, and white Russian tricolors that filled downtown Moscow on Sunday afternoon.

For two nations as intertwined as Russia and Ukraine, the Ukrainian flag has become a political symbol. As strenuously as the Kremlin propaganda machine raises the hobgoblin of Ukrainian nationalism, the conflict between Ukraine and Russia isn’t about ethnicity or language — it’s about the kind of country that people want to live in. Most Ukrainians want to build a Western-style democracy; most Russians are convinced that trying to do the same in their own country would be calamitous, impossible, or both.

As much as Ukrainians may want to step out of Moscow’s shadow, their fate is inextricably tied to Russia’s because Putin is gambling his own political future on their country. Ukraine is so crucial to the Kremlin because of its strategic geographic location. A pliant, easily bribed government in Kiev was the preferred way of controlling Ukraine’s natural-gas pipelines to Europe and keeping the country out of the North Atlantic Treaty Organization.

In Putin’s reverse domino theory, Ukraine had to remain weak, dysfunctional, and divided to be an effective buffer zone. When the Kremlin’s client, then-President Viktor Yanukovych, fled the Maidan protesters in Kiev a year ago, Putin interpreted the change in power as an impermissible encroachment by the West that had be stopped by whatever means possible. While the seizure of Crimea was based on the geopolitical calculation of securing Russia’s Black Sea Fleet base once and for all, Putin cloaked the move in quasi-religious mythology, describing the peninsula as a holy land for Russian Orthodox believers. His use of nationalistic rhetoric fueled separatist sentiment in eastern Ukraine and raised the stature of long-marginalized chauvinists within Russia.

For Putin, the conflict with Ukraine is worth all the risks involved — including damaged relations with the West — as he sees himself in a battle for his regime’s survival. Russian involvement in Ukraine is just a pretext for Western economic sanctions, he said in a nationally televised speech in December.

What happens in Ukraine is also of vital importance to Russian liberals. Like Russians, Ukrainians have struggled with corruption and bad governance, income disparities and a bought judiciary. But in contrast to Russia, political power in Ukraine has been much more fragmented because of regional rivalries and competing oligarchs, creating an opening for ordinary citizens to get involved. Through their civic engagement and willingness to protest, Ukrainians have been a source of inspiration — and envy — to opposition activists in Russia.

The first significant show of people power in Ukraine was the Orange Revolution 10 years ago, when Yanukovych, openly endorsed by Putin, won flawed presidential elections, sparking a non-violent, popular uprising. Pro-Western politician Viktor Yushchenko prevailed in a repeat vote. Russian liberals cheered his victory — and Nemtsov, a reform politician under former Russian President Boris Yeltsin, joined Yushchenko’s team as an adviser.

Putin, on the other hand, became determined not to allow a repeat of the Kiev protests in Russia and began a systematic crackdown on civil liberties. When street protests broke out in 2011 after he had announced his intention to run for a third presidential term, Putin blamed the U.S. State Department for fomenting unrest.

According to the Kremlin, the Maidan protest a year ago was a Western-engineered putsch — and a practice run for the Kremlin. The gloves came off for good.

It’s not a coincidence that a pro-government rally in Moscow on February 22 was called “anti-Maidan.” Demonstrators held up banners that said “Yankee, get out and take Maidan with you!” and “Strong Russia or Maidan?” Some held up a sign with Nemtsov’s picture under the words “Maidan organizer.” A week later, he was dead.

At Sunday’s memorial march, a woman held up a different sign. It read: “The war killed Nemtsov.” She was right.