Schools give patriotic lessons and teach students how to assemble rifles, while textbooks have been rewritten to favor Russia’s view of history. Factories produce uniforms for soldiers fighting Ukraine. Summer camps run by state-owned conglomerates host children from occupied Ukrainian territory.

These by-now familiar scenes would hardly bear mention in wartime Russia, except that these were drawn recently from Belarus, an autocratic country of 9.4 million neighboring Russia, Ukraine and the NATO members Poland, Lithuania and Latvia. Long uneasily in the orbit of President Vladimir V. Putin of Russia, Belarus is increasingly doing his bidding, socially, militarily and economically.

The most recent manifestation of Belarus’s fealty to Moscow — and the threat it poses to the West — is its professed decision to allow Moscow to position tactical nuclear weapons on its soil, as well as outfitting its bombers with nuclear weapons. It is also an important step, democracy advocates and military experts say, toward Russia’s absorption of Belarus, a longtime goal of Mr. Putin.

“Belarus’ sovereignty is evaporating very fast,” said Pavel Slunkin, a former Belarusian diplomat who is now a fellow at the European Council on Foreign Relations. “Any sphere you take, Russia’s control has become extremely big and it’s increasing.”

It wasn’t always this way. Throughout the post-Cold War era, the country’s authoritarian leader, Aleksandr G. Lukashenko, played a clever game, professing loyalty to Moscow and championing the Soviet slogans of the “brotherhood and unity,” while making sure that relations with Moscow never got too close to threaten his hold on power. He even reached out occasionally to Western nations eager to draw Belarus closer to Europe economically.

That arrangement developed cracks in 2014, after Russia seized Crimea, raising the alarming possibility for Mr. Lukashenko that Belarus, too, could be swallowed by its larger neighbor. Mr. Putin reinforced those fears by speaking openly of a political union of the two states.

But it collapsed entirely in 2020, when Mr. Lukashenko cracked down on hundreds of thousands of pro-democracy protesters, making him an international pariah. At that moment of peril, Mr. Putin stepped in, providing cheap energy, an economic lifeline and an implicit assurance of security assistance, should that become necessary.

With Belarus a virtual dependent of Russia, Mr. Lukashenko has become a crucial partner in Russia’s invasion of Ukraine, stopping short only at contributing his own military to the fight.

Pavel Latushka, a former Belarusian diplomat and minister turned dissident, has published evidence that Belarus is complicit in the forced displacement of Ukrainian children from Russian-occupied territory. Prosecutors from the International Criminal Court in March issued arrest warrants for Mr. Putin and his children’s rights commissioner accusing them of deporting thousands of Ukrainian children to Russia.

In late May, Mr. Latushka presented Ukrainian prosecutors with the names and details of approximately a dozen children from Russian-occupied Ukraine who were brought to camps in Belarus. In an interview, he said that as of last month about 2,150 Ukrainian children had been brought to at least three camps run by state-owned companies in Belarus, including the Belaruskali potash company.

Belaruskali was placed under E.U. and U.S. sanctions in the wake of Mr. Lukashenko’s violent suppression of the pro-democracy protests. Ukrainian prosecutors have confirmed that they are investigating Mr. Latushka’s accusations.

Mr. Latushka said he discovered documents signed under the auspices of the “Union State,” a vague alignment of Russia and Belarus, that ordered the movement of Ukrainian children that has been carried out.

The decision is signed personally by Lukashenko,” who currently chairs the supranational body’s leadership council.

The apparent positioning of Russian nuclear weapons in Belarus is also part of agreements made in the Union State, though the Kremlin has said all of the nuclear materials will be under Russian control. The nuclear weapons are a source of pride for Mr. Lukashenko, who thinks they will “give him the ability to stay in power until his death,” said Mr. Latushka.

But they also give Moscow a monopoly of force that diminishes the Belarusian strongman’s control, bring Russia inside Belarus’s borders and posing a potential threat to Belarus’s security — all points that the government’s opponents are trying to drive home to Belarusians.

“We are now ringing all the bells about the deployment of nuclear weapons, which ensures Russia’s presence in Belarus for many years to come,” said Svetlana Tikhanovskaya, Belarus’s primary opposition leader, now in exile.

“Even after the regime changes,” she said “it will be difficult to get rid of them.”

As she spoke, it was three years to the day that her husband, Sergei Tikhanovsky, was arrested on trumped-up charges because he dared to compete against Mr. Lukashenko in the 2020 elections. He was jailed before the vote, prompting Ms. Tikhanovskaya to run in his stead. In December 2021, he was sentenced to 18 years in prison.

His children, now 13 and 7, regularly write to him in jail, but it has been three months since they have heard back. Four of his lawyers have been stripped of their licenses.

A human rights organization, Viasna, has counted 1,495 political prisoners, including its founder, Ales Bialitski, in Belarusian jails. Mr. Bialitski, who shared the Nobel Peace Prize last year with groups from Russia and Ukraine, received a sentence of 10 years last month for smuggling and for financing “actions grossly violating public order.”

Opposition leaders like Ms. Tikhanovskaya — sentenced in March to 15 years in absentia, and Mr. Latushka, who was sentenced to 18 years, also in absentia — have been trying to influence the pro-democracy forces inside Belarus. But it is getting harder, they said, because of the growing prevalence of pro-Russian propaganda. Much of their effort is devoted to warning their countryfolk of the consequences of a potential nuclear strike from Belarusian territory.

“I don’t want to imagine it, but let’s imagine that nuclear weapons will be used at some point when Russia is losing and these weapons fly from Belarus,” she said. “Well, I think there must be some kind of backlash. No one will figure out whether this button was pushed in the Kremlin or in Lukashenko’s palace, right? A retaliatory attack, if there is one, if the West decides what it means to answer, it will fly to Belarus.”

They are also trying to influence Western leaders, and lament that their calls — for now, at least — are mostly falling on deaf ears. The United States and the European Union slapped Minsk with sanctions after the 2020 protests and again when Mr. Lukashenko forced a commercial airliner to land in Minsk because it was carrying a dissident blogger. After Russia invaded Ukraine from Belarus, the European Union — even then its second biggest trading partner — joined the United States and Britain in the most severe sanctions in the country’s history.

But how to react to the latest escalation has become a conundrum for the West.

At a recent conference in Slovakia, President Emmanuel Macron of France called Belarus a “vassal state,” but said Europe bore some of the blame.

“We put him in a situation to be trapped in the hand of the Russians,” Mr. Macron said of Mr. Lukashenko, in response to a question about his current approach toward the country. “If your question is, ‘Do I think we should be more aggressive with Belarus,” my answer is no,” he said, emphasizing that Western leaders needed to offer Mr. Lukashenko an “exit strategy.”

Mr. Macron, who was criticized for making similarly sympathetic remarks about Mr. Putin early after Russia’s invasion, was widely condemned by Belarusian dissidents.

Ms. Tikhanovskaya said it seemed like some Western leaders were “trying to whitewash Lukashenko,” justifying their tepid response out of the belief that he had at least not joined the invasion — though there are allegations that Belarusian officers are training Russian recruits.

Rather than resisting pressure to join forces with Mr. Putin, she said, Mr. Lukashenko was deeply concerned about stirring domestic unrest over a war that remains unpopular in Belarus. If that should spark another major uprising he could be forced to appeal to Moscow for security assistance. And that, Mr. Latushka said, could be the final step toward Mr. Putin’s ultimate goal: “To absorb Belarus.”