A war in Ukraine that began with a Russian debacle as its forces tried and failed to take Kyiv has seemingly begun to turn, with Russia now picking off regional targets, Ukraine lacking the weaponry it needs and Western support for the war effort fraying in the face of rising gas prices and galloping inflation.

On the 108th day of President Vladimir V. Putin’s unprovoked war, driven by his conviction that Ukraine is territory unjustly taken from the Russian Empire, Russia appeared no closer to victory. But its forces did appear to be making slow, methodical and bloody progress toward control of eastern Ukraine.

On Saturday, Ukraine’s agile president, Volodymyr Zelensky, once again promised victory. “We are definitely going to prevail in this war that Russia has started,” he told a conference in Singapore in a video appearance. “It is on the battlefields in Ukraine that the future rules of this world are being decided.”

Yet, the heady early days of the war — when the Ukrainian underdog held off a deluded and inept aggressor and Mr. Putin’s indiscriminate bombardment united the West in outrage — have begun to fade. In their place is a war that is evolving into what analysts increasingly say will be a long slog, placing growing pressure on the governments and economies of Western countries and others throughout the world.

Nowhere is that slog more evident than in Ukraine’s eastern Donbas region. Despite urgent pleas to the West for more heavy weapons, Ukrainian forces appear to lack what it takes to confront Russian use of artillery for scorched-earth shelling of towns and villages. While Ukraine is holding Russia back in the major regional city of Sievierodonetsk, it is suffering heavy losses — at least 100 fatalities a day, though their full extent is not yet known — and desperately needs more weapons and ammunition.

Russia also appears to be making headway in establishing control in towns it has captured, including the leveled Black Sea port of Mariupol. It has set out to convince and coerce the remaining population that its future lies in what Mr. Putin views as his restored empire. Citizens there and in cities like Kherson and Melitopol face a bleak choice: If they want to work, they must first obtain a Russian passport, a blandishment offered to secure a semblance of loyalty to Moscow.

Propaganda that compares Mr. Putin with Peter the Great, Russia’s first emperor, blares from cars in Mariupol in what Petro Andriushchenko, an adviser to the city’s mayor, called a “pseudohistorical” onslaught.

The comparison, one that Mr. Putin has made himself, is dear to the Russian president’s heart. He has repeatedly insisted that Ukraine is not a real nation and that its true identity is Russian. His invasion has, however, cemented and galvanized Ukrainian national identity in ways previously unimaginable.

Russia has its own difficulties, particularly in southern Ukraine, where the provincial capital of Kherson captured earlier in the war is still contested. Attacks by former Ukrainian soldiers and civilians have picked up in recent weeks. Russian losses in the war are not yet known, but certainly run into the tens of thousands, a potential source of anger toward Mr. Putin, whose autocratic hold on Russia keeps tightening.

If the Russian economy has shown surprising resilience, it has been hard hit by Western sanctions; a brain drain will undermine growth for many years. Mr. Putin’s pariah status in the West appears unlikely to change.

Elsewhere, however, in Africa and Asia, support for the West — and for Ukraine — is more nuanced. Many countries see little difference between Mr. Putin’s invasion of Ukraine and the United States’ invasion of Iraq in 2003; they seem unlikely to be persuaded otherwise.

More generally, there is resentment in much of the developing world of what is seen as American domination, viewed as a hangover from the 20th century. In this context, the strong partnership between China and Russia is viewed not with the hostility and anxiety it provokes in the West, but rather as a salutary challenge to a Western-dominated global system.

The American defense secretary, Lloyd J. Austin III, on a visit to Asia to warn of potential Chinese aggression against Taiwan, tried on Saturday to shore up support for the West’s ardent backing of Ukraine against the Russian invasion.

“It’s what happens when big powers decide that their imperial appetites matter more than the rights of their peaceful neighbors,” he said. “And it’s a preview of a possible world of chaos and turmoil that none of us would want to live in.”

Speaking at a security summit in Singapore, Mr. Austin said that Russia’s invasion was “what happens when oppressors trample the rules that protect us all.” He spoke after Mr. Zelensky had expressed concern in his nightly address that the world’s attention may drift away from Ukraine.

With inflation hitting levels not seen for four decades in the United States and Britain, financial markets tumbling, interest rates rising and food shortages looming, such a drift in focus away from a long war toward more pressing domestic concerns may be inevitable. The war is not to blame for all of these developments, but it does exacerbate most of them — and there is no end in sight.

A combination of high inflation and recession, viewed as plausible by many economists, would be reminiscent of the 1970s, when the first oil shock devastated the global economy. With midterm elections in the United States only months away, President Biden and the Democrats can ill afford a campaign season dominated by talk of $5-a-gallon gasoline and near-double-digit inflation.

Yet the ingredients of a long war are clear enough. There is no sign of a Russian readiness for territorial compromise. At the same time, Ukrainian resistance is still strong enough to make any formal cession of territory almost unimaginable. The result is grinding deadlock, a far cry from Mr. Putin’s apparent initial conviction that Russian forces would stroll into Kyiv, Ukraine’s capital, to a warm welcome.

Some of the roots of the war lie in Ukraine’s strategic decision to draw closer to the 27-nation European Union and turn away from Moscow. Mr. Putin could not abide this shift, now reinforced in Ukraine by a brutal confrontation with Russia’s military methods.

Ursula von der Leyen, the European Commission president, met with Mr. Zelensky on Saturday in Kyiv in a show of support. The European Union is considering granting Ukraine the formal status of candidate for E.U. membership at a summit meeting on June 23 and 24. In Paris, there has been talk of a possible visit by President Emmanuel Macron to Ukraine after that meeting.

In Ukraine and beyond, Mr. Macron, who has spoken regularly with Mr. Putin since the war began in February, has been vehemently criticized for insisting on the need to avoid the “humiliation” of Russia in order to keep diplomatic channels open. A French presidential official walked that back on Saturday, saying: “We want a Ukrainian victory. We want Ukraine’s territorial integrity to be restored.”

After the Russian butchery in Bucha, near Kyiv, and in Mariupol, the chances of successful diplomacy appear more remote than ever. It is even unclear what the very term “victory” would mean for either side.