Ukrainian forces tried to seize the battlefield initiative in multiple locations over the winter while struggling to avoid a rout as they pulled out of Kursk, the Russian region they invaded last summer to great fanfare.
Across the 1,100-kilometer front line, Russian troops dialed back their monthslong grinding forward movement, using sodden field conditions to instead replenish unit strength and weaponry stores in anticipation of better weather.
They hammered Ukrainian supply lines in Kursk to push Ukraine's troops back across the border, ending an embarrassing incursion for Russia that the Kremlin was eager to erase.
Now, according to Ukraine's top military officer, Russia has finally begun a new spring offensive in northeastern parts of Ukraine.
Not to be outdone, Ukraine has punched back, reportedly crossing the border in Russia for a second time: into the Belgorod region, possibly with the goal of preempting the spring offensive and keeping Russian troops off-balance.
Lost in the fog of war? Here's what you need to know about where things stand on the ground amid the fourth spring of Russia's all-out invasion.
Guns Of April
For outside experts, the fact that Russian units were prepping for a new push was mostly expected, particularly after a relatively quiet winter.
"It's truly exhaustion in terms of both personnel and armored vehicles, and generally, it's very difficult to be on the offensive for several months, but Russia has been advancing for over a year now," Mykhailo Samus, who directs the New Geopolitics Research Network in Kyiv, told Current Time. "This naturally wears out the armed forces."
On April 9, days after President Volodymyr Zelenskyy warned that Russian forces were mustering for a new push into the Sumy and Kharkiv regions, Ukraine's commander in chief, General Oleksandr Syrskiy, confirmed Zelenskyy's assessment.
"I can say the president is absolutely right, and this offensive has effectively already begun," Syrskiy said in an interview published by the Ukrainian newspaper LB.ua.
"For several days, almost a week, we have observed almost a doubling of the number of enemy attacks in all main directions," he was quoted as saying.
Neither the scope nor scale of the Russian push was clear. The Sumy region borders Kursk, so experts said it would be logical for Russian units to push across the border while Ukrainian troops are on the back foot unable to prepare proper defensive lines.
In Kharkiv, Ukraine's own offensive in late 2022 sweeping across much of the region was a high point for Kyiv. On the region's eastern stretches, however, Russia for months has been chipping away at Ukrainian lines running north-south along the Oskil River, threatening the city of Kupyansk.
Ukraine's second largest city, Kharkiv, has been an unacknowledged priority for Russian commanders, and Russian forces have terrorized the city with missiles and drones.
Further to the south, Russian troops have spent several months inching through the southern suburbs of Pokrovsk, a critical transit hub for Ukrainian defenses in the Donbas region, in what likely is an an effort to encircle the city.
During Russia's winter lull, Ukrainian units managed to push back some of Russian lines outside Pokrovsk. In comments to RFE/RL's Ukrainian Serviceon February 27, Viktor Trehubov, a spokesman for the Khortytsia regional command, claimed Russia's effort to surround Pokrovsk had faltered.
Ukraine's biggest problem has been maintaining troop strength at the front line, hindering its ability to hold back Russia's offenses. Combined, the two sides are estimated by Western officials to have suffered more than 1 million casualties, killed or wounded.
Still, Western military officials have said Ukraine's fighting ability is not entirely spent yet.
"I do not think there is an inevitability to a Ukrainian loss," US Army General Chris Cavoli, who commands US European Command, told a congressional hearing last week. "They are in a much better position than they were."
Russia Invaded: Part II
The invasion of Kursk last August was the largest incursion into Russian territory by foreign troops since World War II. By issuing the orders, Ukrainian commanders hoped to achieve several goals: show they were still capable of creative battlefield tactics; draw Russian troops from elsewhere along the front line, relieving pressure for exhausted Ukrainian defenses; and gain a territorial bargaining chip for future negotiations with Russia.
The first goal was more or less a success, a reflection of the imagination experts say Ukrainian authorities have shown throughout the conflict. The second goal was not successful; instead of drawing units from other locations, Russia commanders deployed parts of existing units along with North Korean troops.
Given that Russia has all but pushed Ukrainian troops out of Kursk, the third goal also appears to have been unsuccessful.
Nevertheless, Ukrainian commanders late last month ordered a new cross-border incursion, this time into Belgorod. The goal, said Ukrainian military expert Oleksandr Musiyenko, is to preempt forthcoming Russian plans.
"We understand that after Russia constantly brings in additional forces to regroup its positions and replenish losses, the risks for Sumy and its city center grow," he told RFE/RL's Ukrainian Service."To counter these risks, we conduct preventive actions to prevent the enemy from rapidly launching their offensive operations."
"This is why we speak of active defense -- to stop the enemy from quickly advancing into Ukrainian territory and minimize the risks to the Sumy region," he said.
For its part, Russia's push into Kharkiv and Sumy may be a reflection of President Vladimir Putin's guidance to his commander in chief, General Valery Gerasimov, last month when Putin visited the Kursk region.
"Of course, I would request that you think in the future about creating a security zone along the border," Putin said.
What About The Cease-Fire?
Last month, the Kremlin and the White House announced the broad contours of a cease-fire, a limited halt to attacks targeting energy infrastructure such as power plants, transmission lines, substations, and similar structures. Kyiv endorsed a limited cease-fire, contingent on Moscow's adhering to it.
Later, there was a tentative agreement to restrict fighting in the Black Sea region, as part of a bid to restart large-scale shipments of Ukrainian -- and Russian -- agricultural goods. The Kremlin, however, insisted on several conditions that outside experts said appeared difficult, if not impossible, to meet.
Now, nearly a month later, the cease-fire has frayed to the point of collapse, as both Kyiv and Moscow continue daily attacks, utilizing scores of drones and powerful missiles. On April 4, a Russian ballistic missile armed with a cluster munition hit the city of Kryviy Rih, an attack Moscow officials said was aimed at a Ukrainian military gathering.
Ukraine, however, said an entertainment venue was hit, along with a playground, resulting in the deaths of at least 20 people, including nine children.
In recent days, US President Donald Trump, who has made resolving the conflict a top priority, has expressed frustration with Russia's continued bombing of Ukrainian targets, including the Kryviy Rih attack.
"I'm not happy about what's going on with the bombing because they're bombing like crazy right now," Trump told reporters on April 7. "They're bombing -- I don't know what's happening there."
