KYIV, Ukraine — There are fields instead of city streets, farmsteads instead of apartment buildings. Open highways stretch to the horizon.
The battles in the north that Ukraine won over the past seven weeks raged in towns and densely populated suburbs around the capital, Kyiv, but the war is about to take a hard turn to the southeast and into a vast expanse of wide-open flatland, fundamentally changing the nature of the combat, the weapons at play and the strategies that might bring victory.
Military analysts, Ukrainian commanders, soldiers and even Russia’s president, Vladimir V. Putin, acknowledge that a wider war that began with a failed attempt to capture the capital will now be waged in the eastern Donbas region.
With few natural barriers, the armies can try to flank and surround each other, firing fierce barrages of artillery from a distance to soften enemy positions.
Russia invaded in February, Ukraine had been fighting Russia-backed separatists there since 2014, when Moscow fomented an uprising and sent in forces to support it. That war had settled into a stalemate, with each side controlling territory and neither gaining much ground.
Now, what may be the decisive phase of Mr. Putin’s latest war is returning to that same region, blighted by eight years of conflict and littered with land mines and trenches, as he tries to conquer the portion of Donbas still held by Ukraine. Neither side has made a major move in recent days, and analysts say it will most likely require a long and bloody conflict for either one to prevail.
Slovakia this week provided Ukraine with a potent, long-range antiaircraft missile system, the S-300. And on Wednesday, President Biden announced an $800 million military aid package to Ukraine that for the first time included more-powerful weaponry, including 18 155-millimeter howitzers, 40,000 rounds of artillery ammunition and 200 armored personnel carriers.