Kasparov rose quickly through the World Chess Federation rankings. Starting with an oversight by the Russian Chess Federation, he participated in a grandmaster tournament in Banja Luka, Bosnia and Herzegovina (then part of Yugoslavia), in 1979 while still unrated (he was a replacement for the Soviet defector Viktor Korchnoi, who was originally invited but withdrew due to the threat of a boycott from the Soviets). Kasparov won this high-class tournament, emerging with a provisional rating of 2595, enough to catapult him to the top group of chess players (at the time, number 15 in the world)). The next year, 1980, he won the World Junior Chess Championship in Dortmund, West Germany. Later that year, he made his debut as second reserve for the Soviet Union at the Chess Olympiad at Valletta, Malta, and became a Grandmaster.