Alekhine left Soviet Russia in 1921 and emigrated to France. In 1927, he became the fourth World Chess Champion by defeating José Raúl Capablanca. Negotiations for a title match with Keres or Botvinnik were halted by the outbreak of World War II in Europe in 1939. In 1946, Alekhine died in Portugal in unclear circumstances. Widely considered to be one of the greatest chess players of all time, Alekhine is also highly regarded as a chess writer and theoretician, having produced innovations in a wide range of chess openings and having given his name to Alekhine's Defence. He is known for his fierce and imaginative attacking style, combined with great positional and endgame skill.