Iceland got through to the quarter-final stage before their fairytale run was ended by hosts and beaten finalists France 5-2.
Serbia qualified for the World Cup for the first time since 2010 by beating Georgia 1-0 in Belgrade with a goal by Aleksandar Prijovic's in the 74th minute.
The European country with the smallest population to take part in the Federation Internationale de Football Association world cup finals are Northern Ireland.
Iceland's Euro 2016 run-in which they shocked the world by making it to the quarterfinals primarily off the back of a stunning victory over England-seemed like it would have been the height of this golden generation's achievements, but that has not proven so.More news: What does Trump want in exchange for letting DACA recipients stay?
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Ireland secured a playoff spot from Group D, while Gareth Bale's Wales was eliminated only 15 months after reaching the semifinals at Euro 2016.
"Are you kidding! We are going to the World Cup!" the local TV commentator bellowed as the final whistle blew and fireworks erupted over the Laugardalsvollur national stadium.
That means the Viking chant popularized by Iceland fans at Euro 2016 will be heard across Russian Federation next year.
The total of 17 points from 10 qualifying matches saw them finish second behind Switzerland and earn a place in the play-offs as the final step ahead of the big event in South Americas.
Having sacked manager Ante Cacic and replaced him with Zlatko Dalic after a disappointing 1-1 draw with Finland on Friday, the Croatians still looked shaky, winning two corners in the first two minutes but doing little else in the opening half.
Iceland's players celebrate after scoring against Kosovo.