Alliance that bombed country only 18 years ago welcomes it as 29th member in move that has left its citizens divided

The Democratic Front, an alliance of parties opposed to Montenegro’s membership of Nato, flies a giant Russian flag from the top balcony of its red-and-white headquarters in Podgorica.

It’s a striking choice given that two of the party’s leaders have been stripped of parliamentary immunity and charged with attempting to overthrow the government in an allegedly Russian-backed plot. But it also shows the deep divisions that continue as the Balkan country of 600,000 is welcomed as the alliance’s 29th member and attends its first summit on Thursday.

It was only 18 years ago that Nato aircraft were bombing targets in Montenegro – then part of a federal republic with Serbia – in a campaign that forced Slobodan Milošević’s troops out of Kosovo. The bombing remains a painful memory for many Montenegrins, and polls have shown the population evenly divided on Nato membership. Then there is the spectre of Russia, a historical ally and fellow Slavic country, accused by the government of an assassination attempt on the then prime minister Milo Đukanović.

“Bombing of a country in the heart of Europe at the end of the 20th century is not something the international community should be proud of,” Đukanović, whose designated successor, Duško Marković, was elected prime minister the day the coup attempt was announced, told the Guardian. “But the last thing that should happen to us in the Balkans is that … due to this episode we forget what the strategic course that we need to pursue is.”

Many hope Nato membership will end the tumultuous east-west struggle in Montenegrin politics, but the divisive trial of the accused plotters starts this week, and the country remains in political crisis.

The ruling Democratic Party of Socialists (DPS) barely gathered enough votes to ratify the Nato accession treaty, and the opposition has promised to call a referendum to reconsider membership if it comes to power. Its leaders have continued to travel to Moscow.

“Russia will continue pressuring and trying to influence the political process in Montenegro,” said the political analyst Zlatko Vujović. “They will have less impact than before because opposition forces are not so strong … but I think they will continue pressuring the opposition political parties.”

One of the key objections to Montenegro’s Nato membership, raised by the US senator Rand Paul among others, is that it can contribute a tiny military of only 2,000 soldiers in exchange for Nato protection. What it does have is the last stretch of Mediterranean coastline between Gibraltar and Syria not controlled by the alliance, a location also coveted by Russia. Moscow asked for but was denied permission to refuel and restock naval ships in Montenegro in 2013, but has denied seeking a permanent base there.

But Nato membership is also a move that has been rejected by much of the population, raising the possibility of continued political upheaval. A poll in December found that 39.5% of the population was for and 39.7% against. Added to 500 who died in the 1999 Nato bombing of Serbia and Montenegro are the historical ties to Russia. Russia was the first foreign country with which Montenegro established diplomatic ties in 1711, and is also majority Orthodox Christian.

“I like Russia, not the Americans. Russia is our people. We have the same culture and history,” said Zhanna Brajović, the owner of a small market in Podgorica.

Since Oleg Deripaska, an oligarch who was close to Vladimir Putin, bought the major state aluminum smelter KAP in 2005, Russian money has been pouring into Montenegro, especially to beachside real estate and development deals. Deripaska is now suing the government over the loss of KAP but remains an investor in the Porto Montenegro yacht marina project. Russia reportedly accounts for one-third of the foreign direct investment in Montenegro in 2015, dwarfing that from western Europe.

Đukanović argued that “Russian investors and tourists find that it is something in their best interest to go to a country which has a rule of law,” which is what Nato and EU reforms, being introduced as it approaches membership, are theoretically achieving.

The Russian government, on the other hand, promised “retaliatory actions” after Nato invited Montenegro. In April, it banned imports from Montenegro’s largest winemaker, and the Russian foreign ministry warned that tourists could “expect provocations and detentions” due to “anti-Russian hysteria”. Russians reportedly accounted for 7.3% of all tourist stays in March, down from 19.2% in March 2016.

The election on 16 October was essentially the last chance for voters to approve or reject Montenegro’s Nato accession. Some accuse the ruling party of unfairly rallying voters to its side by announcing the coup attempt on the day of the polls, even though the alleged plotters were arrested the day before.

“The whole city was in a state of emergency. You could hear the police sirens bringing these guys one by one before the prosecutor,” said Daliborka Uljarević of the Centre for Civic Education. “You feel nervous. It’s not a normal situation.”

In the following months, discussion of the alleged Russian plot has dominated politics and the media, she added.

According to an indictment prepared by the chief prosecutor Milivoje Katnić, a group of Serbian nationalists planned to seize the parliament and assassinate Đukanović, while others dressed as police officers were to open fire on crowds outside. The Democratic Front would be declared the country’s new rulers, stopping the Nato accession process, it said. A member of the group lost his nerve and tipped off law enforcement, who moved in to arrest them.

Two of the 14 charged are alleged Russian intelligence agents being tried in absentia. Serbia arrested the pair with police uniforms, encryption equipment and cash in October. But it sent them back to Russia after the head of the Russian security council visited Belgrade and reportedly apologised for what he described as a rogue operation not sanctioned by the Kremlin. (Belgrade and Moscow have denied this account.)

The main evidence against the indicted opposition leaders, Andrija Mandić and Milan Knežević, is their frequent trips to Russia, and they reportedly visited Moscow again this month. The two deny the existence of any such plot.

“It’s a fake state coup organised by Đukanović … to prevent probable victory of the opposition in the election,” Nebojša Medojević, another member of the Democratic Front, told the Guardian.

Another possibility is that pro-Kremlin radicals did indeed devise the plot. Suspicions fell on Leonid Reshetnikov, the outspokenly hawkish head of a Kremlin-backed thinktank, when Putin fired him a few days after the alleged coup attempt. Also, in a leaked email to an associate of the “Orthodox oligarch” Konstantin Malofeyev, a pro-Russian activist in eastern Europe purportedly discussed the failed Montenegro plot. Representatives of both Reshetnikov and Malofeyev denied any involvement to the Guardian.

In the aftermath of the alleged coup attempt and Montenegro joining Nato, Serbia is likely to become the “main Russian hope in the western Balkans”, according to Andrei Kortunov, director of the Russian International Affairs Council. In the same week that the US Senate approved Montenegro’s Nato membership, the Serbian prime minister, Aleksandar Vučić, and Putin signed the first Russia-Serbia arms deals since 2013.

While many analysts and pundits in Podgorica expect Russia to continue to foment unrest in Montenegro, the political crisis tied to the coup investigation is likely to pose a greater threat to the country’s stability. Vujović said the judicial system and other institutions answered only to the ruling party. “It’s not a black-and-white situation,” he said. “The lack of a real pro-European alternative is maybe a bigger problem.”