This article is part of the Guardian’s 2018 World Cup Experts’ Network, a cooperation between some of the best media organisations from the 32 countries who have qualified for Russia. theguardian.com is running previews from two countries each day in the run-up to the tournament kicking off on 14 June.

Óscar Duarte was born in Catarina, just south of the Nicaraguan capital Managua, but moved to Costa Rica with his mother at a young age. As he developed as a footballer he developed a rare sense of being both a Costa Rican and a Nicaraguan.

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Relations between the countries have not been good for some time and most of the animosity centres on a border conflict at the east end of the two nations and the interpretation of navigation rights on the San Juan river.

In 1998 Nicaragua banned the transit of Costa Rican policemen on the river and this, among other matters such as fishing rights, rumbled on until an International Court of Justice ruling 2009, mainly in Costa Rica’s favour. A year later, however, there was another coming together as Nicaragua dredged 33 kilometres of the river. Costa Rica claimed it was a violation of its sovereignty and had caused environmental damage to the wetlands at Isla Calero.

After five years of diplomatic conflict, the International Court of Justice ruled in 2015 that Nicaragua should pay Costa Rica for the damage. It appeared to be a hollow victory though. Costa Rica had demanded US$6.7m but got US$378,890.

Only last month the ongoing protests in Nicaragua caused renewed diplomatic tension. Officials in San José called on Managua to respect human rights and reconsider the closure of media organisations reporting on the protests. Managua told its neighbour to mind its own business.

All this makes Duarte’s story even more remarkable because the Espanyol defender is one of the few people apparently capable of bringing the two nations together. Ever since his Costa Rica debut in 2010, and particularly after the 2014 World Cup, he has become a symbol of how the two countries can get on.

“It’s nice for me to see how the people come together,” Duarte has said, “because you know all the problems that have happened in the past and all the differences between the two countries, but it’s always nice to show that through football you can make people come together.”

And so it is that on game days the town of Catarina has become an extension of Costa Rican territory, with the residents wearing Los Ticos shirts and celebrating goals as if they were their own. People meet to watch the games together. “We are proud to have a one of our people, such as Óscar Duarte, playing for Costa Rica,” Fermín Guerrero, who lives in Catarina, said. “We feel very happy for him and he also puts the name of Nicaragua on the map.”

Facebook Twitter Pinterest Óscar Duarte is sent off in Costa Rica’s last-16 game against Greece at the 2014 World Cup. Photograph: Brian Snyder/Reuters

Duarte did not have the easiest upbringing but he was determined to become a footballer. It drove him on in the face of adversity. For a long time he flew under the radar. He made his way through the academy at Saprissa, Costa Rica’s most successful club, but did not find it easy to get into the first team and gained experience on loan at Puntarenas.

After that, he returned to Saprissa and enjoyed more playing time before being sold to Club Brugge in Belgium in 2013. He moved to Espanyol three years later and has done well there.

It is, though, as the person who has united two countries in dispute that he stands out. He often goes back to Nicaragua on holiday and was invited to watch the national team play Bolivia around his 28th birthday celebrations. He met the Nicaragua captain, Juan Barrera, beforehand and is friends with another member of the team, Luis Fernando Copete.

Duarte regards himself as representing both countries. “It is not just a feeling,” he told La Prensa last year. “It is the fact that I was born in Nicaragua and no matter what anyone says that is not going to change. I would say that I am representing two countries.”

Asked whether he would be the same person if he had stayed in Nicaragua, he said: “I don’t think so because no one can be the same person if they live somewhere different. If I had stayed in Nicaragua maybe I wouldn’t have had the possibility to move abroad. I was playing for Costa Rica when Club Brugge spotted me, for example.

“I am not surprised that people in Nicaragua cheer me on. I was born in Catarina and I represent both Nicaragua and Costa Rica; I think it’s normal. I do not see why they should miss out on cheering someone in the World Cup just because I have moved to a different country. When you see that these people are happy and grateful that is really nice.”

In Russia Duarte will hope to help Costa Rica reach the quarter-finals again, as they did in Brazil four years ago, but without being sent off, as he was in the last-16 game against Greece. Whatever happens, he has done what few people have done before him: bring Costa Rica and Nicaragua closer together.

Esteban Valverde writes for La Nación.

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