The members of the elite Hungarian police unit crossed the border in civilian clothes, putting on their uniforms only once they had reached their destination. After arriving in Banja Luka, the capital of the Serbian half of Bosnia and Herzegovina, they posed in green fatigues with balaclava-wearing Serbian police.

Officially, the Hungarians had come as trainers, but the mission was announced only after their presence was reported in the local press. The supposedly sovereign Bosnian state government in Sarajevo had not been informed that up to 300 paramilitary police officers from another country would be crossing the frontier.

The timing was key: the Hungarians had arrived on the eve of a pivotal, potentially explosive, date. On 26 February, Milorad Dodik, the firebrand president of the Serb-run republic, Republika Srpska, was sentenced to a year in prison and a six-year ban from holding office for separatist actions.

Dodik, who has run the entity since 2006, was convicted for having defied the envoy of the international community in Bosnia, a position created to ensure implementation of the Dayton agreement that ended the 1992-1995 war. Technically the supreme power in the country, the high representative has the power to impose or annul laws and sack officials.

Responding to the ruling, Dodik told his supporters the conviction was “nonsense” and called on them to “be cheerful”. He then said that Bosnia and Herzegovina had “ceased to exist” and, in an apparent move towards secession, had local laws passed that ban the presence of national law enforcement or judicial officials on Republika Srpska soil. Dodik insisted he would not appeal against the verdict as he did not recognise the court’s jurisdiction, but noted he could not stop his lawyers appealing. The lawyers did so and the appeal is due to be heard in the next few months.

The verdict and Dodik’s response represented a moment when Bosnia’s long-term dysfunction tipped into a dangerous crisis, that could split Europe. It showed that in a squeeze, the Hungarian prime minister, Viktor Orbán, would actively side with Vladimir Putin and allies such as Dodik rather than Brussels. During almost two decades in power, Dodik has been a frequent visitor to Moscow, showing up there on Tuesday for the third time since March.

Serbia’s authoritarian president, Aleksandar Vučić, also routinely backs Dodik in his standoff with Sarajevo and western capitals. Vučić went to Banja Luka in solidarity, after what he called the court’s “unlawful, anti-democratic” verdict. The two men met again in Belgrade on Monday, as Dodik made his way to Moscow.

The ruling and its aftermath also showed that, 30 years after conflict in Bosnia killed more than 100,000 people, its underlying divisions are far from being resolved. Few expect a return to war, but the country remains a flashpoint in the heart of Europe with potential for strife and violence.

The war that was ended by the Dayton accords was a horrendous conflict that brought genocide back to the heart of Europe. The accords will be commemorated this week by a Nato meeting in the Ohio city that gave the peace deal its name. But while Dayton stopped the killing, it also simply froze the conflict by splitting the country into two halves: Republika Srpska and a Federation of Bosnian Muslims (Bosniaks) and Croats.

Dayton’s critics denounced it as a reward for ethnic cleansing. The bandage that stemmed the bloodshed has hardened over the decades into a straitjacket that has prevented Bosnia from developing into a functional state. It established a multi-tiered system of governance that favoured nationalist parties, paralysis and corruption.

Since coming to power, Dodik, the Republika Srpska president and leader of the Alliance of Independent Social Democrats, has blocked reforms and European integration with threats of secession and a return to conflict. But there are signs he is growing politically more frail: Bosnian officials and foreign diplomats in Sarajevo confirmed reporting in the Hungarian press that said Orbán’s paramilitaries had been in Banja Luka to extract Dodik if he found himself cornered and had to make a run for it.

That has not happened yet, but experts say Dodik’s departure remains a strong possibility: in the past few months, the Serbian leader’s family has approached a senior western official to negotiate terms for his departure, the Guardian has been told..

But it is not a foregone conclusion that Dodik will choose exile. Instead, he may continue to try to defy the sentence – and international community – and cling to office behind a shield of his paramilitary police. For the country itself, the limbo is full of risk. “It’s very clearly the most dangerous moment in Bosnia since 1995,” said Jasmin Mujanović, a Bosnian political analyst. “It’s a crisis that can only end with his arrest or if he opts ultimately to flee.”

There was an attempt to detain Dodik in April, after the passage of legislation deemed extreme even by his standards. The Bosnian prosecutor issued arrest warrants for him and two other Serbian officials, and six weeks later there was a tense standoff in east Sarajevo, when Serbian police prevented agents of the Bosnia State Investigation and Protection Agency (SIPA) from arresting Dodik. The SIPA agents withdrew.

The appeal judgment on the February verdict is due by the end of the year but it is generally expected by the summer. If it upholds Dodik’s conviction and sentence, the ban on holding office would take effect, potentially triggering new presidential elections in Republika Srpska and the possible victory of an opposition coalition prepared to collaborate against ethnic boundaries and revive Bosnia’s EU membership bid.

It could also mean that another, more determined, attempt may be made to arrest him, and Bosnia could ask the small European peacekeeping force, Eufor, for at least a show of support.

“The only mystery is whether Dodik will accept the ruling and leave his premises in the presidential palace,” said Igor Crnadak, a former Bosnian foreign minister and senior member of the Party of Democratic Progress, part of the Serb opposition bloc. “Or will he refuse to leave his position? I don’t think anybody knows what he will do.”

He added: “I think that Bosnia is at the turning point.”

Christian Schmidt, a German former minister serving as the current high representative, insists that, for now, it is a political rather than security crisis.

“How do we solve this kind of challenge without an escalation? I think this is something which needs a lot of diplomacy and talks behind the scenes for the moment,” Schmidt said, but he added: “I do not see that Mr Dodik meets the requirements for a responsible member of the political leadership in this country.”

Last week, Schmidt reported to the UN security council on the worsening situation and appealed for international engagement to forestall a disaster. The signs at the council meeting were not encouraging. The Russian delegation left the chamber while Schmidt was speaking, and the Serbian member currently holding the chair in Bosnia’s rotating trilateral presidency, Željka Cvijanović, flew in for the occasion to try to turn the tables on Schmidt, questioning his legitimacy and accusing him of “dictatorship” and “repression”.

At the EU level, action has also been limited. Hungary has so far blocked sanctions against Dodik, with help from Croatia.

The financial pressure on Dodik is mounting, however. The US, UK, Germany, Austria, Poland and Lithuania have all taken individual punitive measures against him. His hope that Trump’s restoration to power in Washington would lead to a swift suspension of US sanctions has not been fulfilled; the new administration has little interest in Bosnia.

If his appeal fails, Crnadak suggested he follow the same advice Dodik once gave to the Bosnian Serb wartime leaders when they were on the run from the war crimes tribunal in The Hague: give yourself up.

“What you are doing now is directly affecting Serbian people and Republika Srpska,” Crnadak said. “If you love your people, you will go to the court and fight for your innocence there.”