What must happen for peace to come to Ukraine?

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(CNN) --

This weekend marks two years since Russia invaded Ukraine, a conflict that has claimed tens of thousands of lives, upended long-standing international norms and has no clear end in sight.

In more ways than one, Russia's President Vladmir Putin has failed: Ukraine remains a sovereign nation, with Moscow in control of about a fifth of its territory, but far from his goal of overthrowing his government.

Putin wanted to stop the expansion of NATO: he now faces an alliance that has added hundreds of kilometers to its border with Russia after the accession of Finland.

But as the war enters its third year, there are increasing signs that it is shifting in Russia's favor, both on the battlefield and in terms of the decline of once-solid Western support.

Below, a look at some of the most significant moments of the war so far.

February 24, 2022: start of the "special military operation"

Two years ago, Putin announced early in the morning a "special military operation" against Ukraine, a euphemism he still frequently uses to refer to an all-out invasion of the country.

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Putin said he wanted the "denazification" of Ukraine, one of his justifications for the invasion that analysts say distorts history.

Moments later, the first explosions were heard throughout Ukraine.

Although Western intelligence services had been warning of an imminent Russian invasion for months, the announcement caught many by surprise.

Putin's announcement marked the start of Russia's war in Ukraine, which has so far cost the lives of more than 10,300 civilians, according to the United Nations.

Military losses are more difficult to determine, but Russia is believed to have had more than 300,000 dead and wounded.

February 26, 2022: "I need ammunition, not to be taken away": Ukraine indicates that it will not be intimidated

Ukrainian President Volodymyr Zelensky posted a video on Facebook on Friday, February 25, vowing to defend his country while standing on a Kyiv street with other leaders of his administration.

"We're all here," he said.

"Our army is here. Citizens and society are here. We are all here defending our independence, our state and it will remain so. Glory to our defenders! Glory to our defenders! Glory to Ukraine!"

(Office of the President of Ukraine)

Ukrainian President Volodymyr Zelensky was in Kyiv when Russia invaded the country, and Putin's forces were expected to advance rapidly on the capital.

Two days later, he rejected an evacuation offer from the United States.

With defiant words, he told the Americans: "I need ammunition, not to be taken away."

His attitude revealed his country's fighting spirit in the face of Russian aggression and its determination not to crumble as some expected.

The Ukrainian defenders of Snake Island—a tiny island in the Black Sea—echoed this challenge early in the war when, outnumbered and ordered to surrender, they responded to a ship's warning. approaching Russian military saying: "Russian warship, go to hell."

The phrase has since been adopted as a slogan during the war and used by protesters in solidarity protests with Ukraine in the West.

March 16, 2022: Mariupol theater bombing

Painted on the ground outside the Drama Theatre, in giant Cyrillic letters, was the word "CHILDREN".

The message was large enough to be seen from the sky.

Throughout the conflict, Russia has carried out a relentless bombing campaign, with one of the worst examples coming when the Mariupol Drama Theater was hit by Russian forces.

It is estimated that some 1,300 civilians were sheltering inside the theater when it was attacked.

Painted on the ground outside the building—in giant Cyrillic letters visible from the air—was the word "CHILDREN."

About 300 people are believed to have died there, according to Ukrainian authorities.

CNN has not been able to independently verify the death toll.

Since then, there have been numerous high-profile Russian attacks against civilian targets.

More than 40 people were killed in an attack on an apartment block in Dnipro in January 2023. At least 51 people were killed when Moscow forces attacked a cafe and shop in Hroza, Kharkiv region, in October 2023.

April 1, 2022: atrocities in Bucha

The following month, a small town west of Kyiv became synonymous with war crimes.

International experts stated that they had found "serious violations" of international humanitarian law by Russian forces when they withdrew from the city of Bucha.

Residents told stories of ransacked homes, murders and failed escapes.

The city mortuary ran out of space.

Some residents described how they had turned their orchards and front yards into makeshift graves, as the presence of Russian forces prevented them from transporting their dead.

The evidence of the executions was clear when bodies were found with their arms tied behind their backs and multiple gunshot wounds.

April 14, 2022: Sinking of the Moskva

Early on Monday, April 18, 2022, images appeared on social media of the Russian guided missile cruiser Moskva severely damaged and set on fire hours before its sinking in the Black Sea on Thursday.

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The Russian warship Moskva, flagship of the Russian Navy's Black Sea Fleet, sank on April 14.

The reason for this was disputed.

Ukraine claimed it had hit the ship with anti-ship cruise missiles, while Russia insisted a fire caused it to sink.

In any case, the sinking was a great embarrassment for Russia, which suffered the largest loss of a warship in 40 years.

It was an early sign of how the Black Sea would become an important front.

In October of that year, Ukraine attacked the only bridge connecting annexed Crimea to mainland Russia and has been harassing the Russian Black Sea Fleet, claiming to have destroyed a third of its ships.

November 9, 2022: The liberation of Kherson caps a successful autumn

There were scenes of euphoria when the city of Kherson was liberated after eight months of Russian occupation.

The withdrawal dealt a serious blow to Putin's war effort: Kherson was the only Ukrainian regional capital that Russian forces had captured since the February invasion.

The withdrawal of Russian troops eastward across the Dnipro River capped a successful autumn for Ukraine, which regained swaths of land Russia had occupied since the early days of the war.

Despite successes on the battlefield, the colder months brought new danger when Moscow's aviation began bombing the country's energy grid in an attempt to undermine morale.

Millions of civilians were left without electricity, heat, water and other critical services during the winter.

May 3, 2023: Drones attack the Kremlin and war comes to Russia

In the spring of 2023, an emboldened Kyiv increasingly brought the war to Russia, with a series of drone strikes on Russian soil.

The attacks hit cities such as Moscow.

On May 3, two explosive drones targeted the Kremlin, in the heart of the capital.

They were intercepted and destroyed before causing damage or injuries, according to the Kremlin.

Ukrainian authorities denied involvement.

That same month, Russia blamed Ukraine for another drone attack on Moscow, which injured two people and damaged several buildings.

Putin called the attack a "clear sign of terrorist activity," while a spokesman for the Ukrainian air force said it was aimed at Russians who felt the war was distant.

There have been subsequent attacks, such as against oil facilities and other infrastructure.

This year, Russia evacuated some residents from the Belgorod border region following an increase in deadly Ukrainian attacks.

May 20, 2023: Russia takes control of Bakhmut

A Ukrainian soldier (L) looks with glasses next to another (R) sitting on an anti-aircraft gun near Bakhmut, on March 24, 2023. (Photo by ARIS MESSINIS/AFP via Getty Images)

After months of fighting for every inch of territory, Russia captured the besieged eastern city of Bakhmut.

The fight for the city—whose symbolism outweighed its strategic importance—encapsulated the slowness of the ground war, which had come to resemble the type of fighting of the First World War.

Moscow poured enormous amounts of manpower, weaponry, and attention into the city, but struggled to put down stubborn Ukrainian resistance, which exceeded all expectations.

The Russian victory came at an enormous cost.

A NATO source told CNN that they estimated that for every Ukrainian soldier killed defending Bakhmut, Russia had lost five.

June 2023: Ukrainian counteroffensive

After months of preparation, Ukraine began a counteroffensive aimed at reconquering territory occupied by Russia.

With fighting focused on the southern and eastern fronts, its launch brought with it a renewed sense of optimism.

However, Russia had had time to prepare layers of defenses.

As the months passed, it became clear that the counteroffensive would not provide the decisive breakthrough that many had hoped for.

For example, the fighting around Robotyne, north of Mariupol, was characterized by crawling over vast minefields, where troops fought for limited gains in streets or even buildings.

The counteroffensive had stalled with the return of winter, and Western intelligence assessments warned that the battlefield could become stagnant, turning the war into a "frozen conflict."

June 23, 2023: Wagner Mutiny

Yevgeny Prigozhin was the founder of the Russian private military group Wagner, which played a crucial role in Bakhmut.

In his day he was close enough to Putin to be called his "personal chef."

But everything changed on June 23, when Prigozhin led an armed insurrection against Putin after railing against the country's military leadership for its handling of the Ukraine war.

His group began marching towards Moscow, shooting down military planes and killing Russian soldiers.

But he stopped abruptly when Belarusian leader Alexander Lukashenko negotiated a deal.

Criminal charges against Wagner's boss were dropped, but Putin said in a speech that those who followed the "path of treason" would be punished.

Months later, Prigozhin died when the plane he was traveling in crashed northwest of Moscow.

January 2024: US aid stalls

The constant trickle of aid from Western countries, particularly the United States, as well as the supply of modern weaponry have proven to be a vital lifeline for Ukraine in its war.

But in early 2024, a US aid package for Ukraine stalled.

The US Senate passed a $95.3 billion foreign aid bill with bipartisan support, including $60 billion to support Ukraine.

However, Republican House Speaker Mike Johnson has resisted a quick vote, which would likely face a revolt from members of his own party.

The episode is a reminder of how Ukraine's destiny is not entirely in its own hands.

Ukrainian commanders have warned of critical ammunition shortages hampering their fight.

February 8, 2024: dismissal of the Ukrainian military chief

Valerii Zaluzhnyi pictured at a ceremony commemorating Ukraine's Independence Day in Kyv on August 24, 2023. Credit: Sergei Chuzavkov/AFP/Getty Images

This month, Zelensky announced the dismissal of Ukraine's top commander, Gen. Valerii Zaluzhnyi, in the biggest military shakeup since the start of the full-scale Russian invasion nearly two years ago.

It is known that both were at odds and their dismissal represented a political gamble for Zelensky.

Despite the failure of the Ukrainian counteroffensive, the now former military chief remains one of the country's most popular leaders.

The move also came as Ukraine found itself back in a defensive position due to a wave of Russian offensives along much of the front line.

On February 17, Russia declared that it had taken full control of the eastern city of Avdiivka, marking Moscow's biggest victory since Bakhmut.

As the war enters its third year, the future of the conflict is even more uncertain.

CNN's Jennifer Hauser, Victoria Butenko, Daria Tarasova-Markina and Andrew Carey contributed to this report.

Russian war in Ukraine