By Marc Santora and Andrew E. Kramer

KYIV — In forests, in fields and in fierce urban combat, the Ukrainian military has defied the odds, and all expectations, and forced Russia into multiple retreats over nine brutal, bloody months of war.

And yet despite its success, and even with tens of thousands of soldiers killed on each side, Ukraine by one measure is only halfway done: Its army has now reclaimed about 55% of the territory Russia occupied after invading in February.

Ukraine is on the offensive along most of the 600-mile front line. Russia is in a defensive crouch in the south and northeast while still attacking toward one eastern city, Bakhmut.

Ukraine’s success has brought the war to a pivotal juncture. Because it is on the offensive, it can shape the next phase of the fighting, determining whether to push its advantage farther into Russian-occupied territory, or settle in for the winter, as military analysts say Russia would like to do.

Should it press on, Ukraine faces significant hurdles: While it has pushed more Russian fighters into a tighter space, this means the battles ahead will be against more densely defended territory, on challenging terrain.

Ukraine is now fighting in boats in the reedy marshes and deltaic islands of the lower Dnieper River; it is pushing against multiple trench lines on snowy plains in the Zaporizhzhia region in the south; and is engaging in a bloody, seesaw fight along the so-called Svatove-Kreminna line, in pine forests in northeastern Ukraine.

After the Russian withdrawal from Kherson this month, President Volodymyr Zelenskyy of Ukraine made a dramatic visit to the city, the only provincial capital captured by Russian forces. Raising the Ukrainian flag over a government building, he echoed a famous speech by Winston Churchill after the British victory at the Second Battle of El Alamein in 1942.

Churchill had declared “the end of the beginning” to the conflict, which would drag on for three more years. Zelenskyy tried to flip the narrative.

“This is the beginning of the end of the war,” he said.

Still, about one-fifth of Ukrainian territory remains occupied by Russia.

A Reshaped Front

The winter war, after Ukraine liberated the city of Kherson and surrounding areas earlier this month, is beginning now with a radically altered front line and a Russian army that is demoralized and degraded.

“Russian ground units have suffered from low morale, poor execution of combined arms, subpar training, deficient logistics, corruption, and even drunkenness,” wrote Seth G. Jones, the director of the International Security Program at the Centre for Strategic and International Studies, a Washington-based think tank.

Ukraine’s advances mean more of Russia’s supply lines in southern Ukraine are now within range of Ukrainian guns and rockets, and Kyiv says it will keep firing on them.

But the new geometry also creates advantages for the Russians, whose pullback from Kherson this month was their third major retreat of the war — but one that moved their forces to more defensible positions on the eastern bank of the Dnieper River.

The Russians continue to send newly mobilized soldiers to Ukraine to make up for steep losses. The tens of thousands of Russian soldiers withdrawn from the Kherson region west of the river are freed up for redeployment, to reinforce defensive lines in the northeast, mount new attacks in the Donetsk region and fortify Moscow’s hold on the land bridge from Russia to Crimea that is so important to the Kremlin.

While military analysts frequently note that the winter weather — the first snowstorm blew over the trenches this weekend — will likely slow the pace of Ukrainian offensives, it will also certainly take a toll on poorly equipped Russian soldiers. And yet the war began in the winter last February, and both armies have extensive experience fighting in wintertime on the Eurasian steppe.

A Separate War, on Infrastructure

While Russian soldiers are on the defensive on battlefields in the south and east, Moscow has opened what amounts to a separate war: missile and drone strikes aimed at destroying Ukraine’s infrastructure, degrading the quality of life for millions of civilians in an effort to demoralize them.

Last week, Russia launched its largest bombardment of the war aimed at power plants, substations, natural gas facilities and waterworks — a sustained campaign of devastation rarely attempted before.

Col. Yuriy Ihnat, a spokesperson for the Ukrainian air force, said Monday (21) that the military has “autonomous power sources,” so that problems with the national grid do not directly impact soldiers on the front. And he said the attacks provide motivation for soldiers who have families enduring the hardships, strengthening their resolve to fight.

But the strikes are a drain on Ukraine’s air defence system, Ihnat acknowledged. He said Ukraine shoots, on average, two missiles at each Russian rocket in hopes of increasing its chance of success, and now it needs more ammunition and air defence systems to keep up. Additionally, he said, Russia is using relatively cheap drones to exhaust Ukrainian air defences.

Ihnat said this weekend that the missile bombardments are meant to force Kyiv to the negotiating table.

“It is clear they want to impose certain conditions, they want to make us negotiate,” he said.

The Kremlin has acknowledged as much. Dmitry Peskov, the Kremlin spokesperson, told reporters last week that the infrastructure strikes are “the consequences” of Ukraine’s unwillingness to “enter into negotiation.”

Ukraine Strikes Deep in the South

Despite Russian threats, officials in Kyiv say they are in no mood to negotiate, hoping instead to use the momentum of the fall offensives to keep Russian forces on the back foot.

Ukraine’s military said last week that Russian soldiers were already retreating 10 to 15 miles from the eastern bank of the Dnieper River near Kherson, to move out of Ukrainian howitzer range.

As things stand, Ukraine’s precision, long-range missiles can now reach deeper into Russian controlled territory, with nearly everything north of Crimea within range. In a reflection of their changing fortunes, the Russians are now digging trenches in northern Crimea, the peninsula they annexed in 2014.

The Russians are also adding new layers of defences outside the southern city of Melitopol, which was occupied by Russia in the first days of the war. It sits at the crossroads of the main highways in the south, making it perhaps the most strategically important city under Russian control.

Military analysts have speculated that Ukraine may try to divide Russian forces in the east and south by driving through Melitopol.

Bloodshed in the Donbas

The rolling plains, coal mining and farming towns of the Donbas region of eastern Ukraine remain contested ground — and an area where Russia is seeking to turn the tide of its failures.

According to Gen. Oleksiy Hromov, a member of the Ukrainian general staff, the eastern front remains the most challenging in the country. Between Nov. 12 and 17, he said, the Ukrainian military reported more than 500 military clashes in the region.

The Donbas has divided into two battles: One is a trench line through pine forests along a critical supply route known as the Svatove-Kreminna line, for the two largest towns in the area. The other is a battle for Bakhmut, a city in a bowl-like river valley, with each side holding heights. The city and nearby villages have become a shooting gallery for artillery.

Bakhmut has limited strategic value, but the fighting is fierce for several reasons. For Russia, capturing it could open a pathway to other more important cities in the Donbas. Beyond that, Bakhmut is viewed as a trophy by the Russian private military contracting company, Wagner, which has sought to seize it as a way to compensate for losses elsewhere and to buoy the political fortunes back in Russia of the company’s founder, Yevgeny Prigozhin.

Ukraine, for its part, has been reluctant to yield any city without a fight — witness its months-long battle over Sievierodonetsk, a city nearby Bakhmut and ultimately taken by the Russians, and Mykolaiv in the south, still held by Ukraine.

-New York Times