After stunning Ukrainian counter-attacks forced Russian invaders into humiliating retreat on several fronts in the second half of 2022, Moscow has rebounded with small but steady advances in eastern Ukraine as the war marks its first anniversary.
Following are some of the major developments in Europe's biggest conflict since World War Two.
THE INVASION
Russian President Vladimir Putin ordered tens of thousands of troops into Ukraine on a "special military operation" to "disarm" the country, purge "nationalists" and halt what Moscow calls Western encroachment through NATO and European Union support of Kyiv. They attacked from the north, east and south.
Ukrainians say Putin aims to subdue their country - like Russia part of the Moscow-led Soviet Union until its 1991 break-up - and erase their 1,000-year national identity.
RUSSIA FAILS TO TAKE KYIV
Within hours of the invasion, Russia landed commandos at Antonov airfield, a cargo base just north of Kyiv, as part of plans to seize the capital. Within a day, Ukrainians had wiped out the elite Russian paratroopers and destroyed the landing strip. Russian armoured columns reached the northern outskirts of Kyiv but eventually beat a chaotic retreat.
ATROCITIES
Russian forces killed at least 441 Ukrainian civilians in the early days of the invasion, including by summary execution in what might amount to war crimes, United Nations human rights investigators reported later in the year.
The killings occurred in the Chernihiv, Sumy and Kyiv regions, most notoriously in the Kyiv satellite town of Bucha, until early April when Russian forces withdrew, the Office of the High Commissioner for Human Rights said.
Moscow has repeatedly denied deliberately attacking civilians in the conflict, contending that evidence presented was staged.
RUSSIA CHANGES TACK
In March 2022, Russia scaled back its stated war goals, saying it would focus on completely "liberating" Ukraine's eastern Donbas region, where Moscow-backed separatists rose up in 2014.
Russian forces made slow, steady gains in a phase of the conflict that inflicted a heavy toll on both sides. By June, the Ukrainian government said 100-120 of its soldiers were being killed every day. Russia did not disclose daily casualties.
Russian troops used superior artillery firepower to hem in Ukrainian forces. After capturing the Donbas cities of Sievierodonetsk and Lysychansk, Putin declared a victory in the area on July 4, though fighting went on.
For Kyiv, a morale-boosting moment came on April 14 when two Ukrainian missiles hit Russia's Black Sea Fleet flagship Moskva, the biggest warship sunk in combat for 40 years.
SIEGE OF MARIUPOL
Russia captured the key Black Sea port city of Mariupol in May after a three-month siege the Red Cross called "hell".
At one point in March, a theatre where Ukraine said families were sheltering in a basement was destroyed. The word "children" painted on the ground outside could be seen in satellite photos. Kyiv says Russia bombed it, killing hundreds. Moscow said, without giving evidence, that the incident was staged.
The siege ended when the last Ukrainian defenders, holed up inside the giant Azovstal steelworks, surrendered.
UKRAINE COUNTER-ATTACKS
As the war churned on, the United States and Europe began giving Ukraine increasingly powerful and longer-range weaponry and used sanctions to try to hamper Russia's military machine.
In August, a better-armed Ukraine launched a southern counter-offensive around Kherson, Russia's only land bridge to Crimea, which it seized from Ukraine in 2014 and is the home of its Black Sea Fleet. Kyiv carried out strikes on Russian supply lines, ammunition dumps and even the Saki air base in Crimea.
In early September, Ukrainian forces reeled off unexpected gains in the northeastern Kharkiv province, wresting back the sole rail hub supplying Russia's front line in the region.
RUSSIA ON THE BACK FOOT
With Russia's invasion clearly faltering, in September and October it drafted some 300,000 reservists to solidify its hold on remaining occupied territory, about a fifth of Ukraine. Military experts, who once doubted Kyiv could hold out for more than a few days, discussed whether Russia could still win the war.
RECAPTURE OF KHERSON
On Nov. 9, Russia ordered its forces to abandon Kherson, the only regional capital it had taken. Joyous residents feted the return of Ukrainian forces, though the city remains subject to Russian shelling. The Kherson region was one of four Putin had declared incorporated into Russia "forever".
RUSSIAN MISSILE BARRAGE
Since the last months of 2022, Russia has unleashed scores of missiles at Ukraine's energy infrastructure, plunging millions of Ukrainians into darkness and cold.
Moscow says it is attacking facilities critical to Ukraine's war effort; Ukraine says the strikes far from eastern and southern front lines only serve to harm civilians, and amount to war crimes.
NEW RUSSIAN OFFENSIVE TAKES SHAPE
After months of static artillery battles and grinding trench warfare in which front lines hardly budged, Russian forces reinforced by tens of thousands of fresh recruits and Wagner mercenaries began inching forward again in January.
On Jan. 13, Russia announced the capture of the salt-mining town of Soledar in Donetsk province, with Wagner fighters playing a pivotal role - Moscow's first notable battlefield success in half a year.
Russia is now focusing on the nearby city of Bakhmut, much of it razed by months of bombardment that have driven out most of the pre-war population of 70,000.
Between Feb. 7 and Feb. 12, Wagner forces appeared to have advanced several kilometres around the north of Bakhmut and begun to encircle it - a rapid push in a battle where front lines had been frozen for months.
Ukrainian President Volodymyr Zelenskiy said Russia was in a hurry to gain ground in the east and south before Kyiv receives modern battle tanks and other potentially game-changing heavy weaponry from NATO and other Western supporters.
Ukraine is using shells much faster than the West can make them, and NATO has begun discussing its request for fighter jets and long-range missiles to go with promised tanks for a counter-offensive widely anticipated to unfold in the spring.
BIDEN VISITS KYIV
With the war's first anniversary in focus, on Feb. 20 U.S. President Joe Biden made an unannounced visit to Ukraine, taking a 10-hour train journey to walk through Kyiv with Zelenskiy while air raid sirens blared, and promising to support Ukraine for "as long as it takes".
The next day, Putin announced in his state of the nation address that Russia would suspend its last major nuclear arms control treaty with the United States; Biden, in Warsaw, responded in an open-air speech, saying: "Our support for Ukraine will not waver, NATO will not be divided, and we will not tire."
UNITED NATIONS
On Feb. 23, the United Nations General Assembly adopted a resolution by 141 votes to seven demanding that Russia quit Ukraine and agree a "comprehensive, just and lasting peace". Belarus, North Korea, Eritrea, Mali, Nicaragua and Syria backed Russia, while China abstained.
Click on the link to listen to the Reuters World News Podcast Special anniversary episode: The Ukraine war
(Writing by Peter Graff, Mark Heinrich and Kevin Liffey; Editing by William Maclean)
