Eight days later, that bucolic life shattered when Russia invaded Ukraine, and Pozniak was thrust into Europe’s most brutal war in generations. It was a dizzying change from being a high-flying investor.

“After February 24, it became a different life,” he told Fortune, by Zoom from his military unit near Studenok, in the eastern Ukraine region of Donetsk. Speaking over the loud booms of explosions from Russian artillery close by, Pozniak, 47, said, “There are two different universes, and this is now my universe.”

It is also the universe for other Ukrainian business leaders. After years building lucrative careers and comfortable lives, many have joined the war since it began three months ago, upturning Ukraine’s dynamic corporate world—and potentially worsening its dire economic crisis; the World Bank estimates the country’s GDP could contract about 45% this year.

What is more, the execs-turned-soldiers say their war experience has left a deep mark that will far outlast the conflict—and impact their businesses.

Juggling war and business

During a weeklong visit to Ukraine by Fortune, and over Zoom from the warfront, executives described trying to keep their businesses going while they are off fighting the war.

Pozniak says his company, with assets of about $25 million, shut its doors when Russia invaded and reopened two weeks later using the few staff left in Kyiv. He, meanwhile, spent the first month of the war with a combat unit, fighting off Russia’s advance on the capital, and then deployed to eastern Ukraine, where Russia has mounted a ferocious assault in an effort to capture territory.

But for many, juggling combat and business has become almost impossible.

“Most businesses have partially or completely stopped,” said Serhiy Haydaychuk, president of Ukraine’s CEO Club, over coffee in the clubhouse overlooking Kyiv. Many of his organization’s more than 200 members have left to fight, he says.

Body-armor factory in two weeks

The club divided its members into groups, each with a specific wartime role, like logistics, procurement, or fundraising. When Ukraine’s government reported a severe shortage of body armor for soldiers, the members opened a factory to make bullet-proof vests, producing 30,000 of them in two weeks, for about $150 each—about one-quarter the cost of imported Western versions.

“We have to be creative,” Haydaychuk said. “We do not have time to think and wait.”

Indeed, all that has happened even as businesspeople have left to fight the war.

As a result, Haydaychuk and others believe that, having proven their worth on the battlefield, Ukraine’s business leaders will likely push hard for change in the country once peace is restored.

“Over the past 30 years, I would say, government was never a partner for business,” Haydaychuk said. “Mostly it was against businesses.” He cited years of rules and regulations decided unilaterally by successive governments, without consulting executives.

He believes that could finally change when there is peace. “Given the incredible shock of the war, is it a good moment to actually start from scratch or to start doing things in a different way,” he said.

Warfront birthday

These execs-turned-soldiers describe the war as a pivotal moment in their lives.

One of them is Serhiy Zhuykov, managing director of Blackshield Capital Group, an investment firm in Kyiv with more than $500 million in assets under management.

Zhokov had lived a good life until Feb. 24, and had purchased air tickets to Spain to celebrate his 40^th birthday in early March with his wife and two teenage children.

Instead, he marked that milestone fighting outside Kyiv.

With no military experience, he underwent combat training near the Belarus border, and on Wednesday, was preparing to deploy to eastern Ukraine. “A lot of people have left their jobs to fight: Small businesspeople, managers, lawyers,” said Zhuykov, whose hometown of Kherson in southern Ukraine was captured by Russian forces early in the war.

He says executives like him, with no prior experience of war, have been profoundly impacted by three months of combat, with bonds that will extend from the conflict, to business.

Outsiders and insiders

“It will really change the business community,” he said. “People who decided not to help will become outsiders in the business community. [And] those who joined the military or helped in some way will work more closely together.”

Courtesy of Serhiy Zhuykov

That is also the case for Volodymyr Tereshenko, managing partner of Energy 365, a Kyiv-based electricity and gas supplier to businesses.

Speaking from Sloviansk, in eastern Ukraine—the scene of weeks of fierce battles—Tereshenko, a former military officer who is now in Ukraine’s National Guard, says his unit has faced intense shelling, at times suffering continual bombardment for days.

“The situation is extremely hard right now,” he told Fortune from the frontline in a Zoom call over Starlink satellite. He says he has instructed his staff to run the company in his absence. “That helps me to totally concentrate on fighting the war,” he said.

Tereshenko, who turned 46 on Wednesday, said he had hoped to celebrate his birthday with victory over Russia. Instead, he says he received an unexpected birthday gift, when two members of his combat unit, who were thought to have died in battle, were found alive on Wednesday in a Sloviansk hospital.

“I am a pacifist,” he said. “My mission is to finish this war.”