of Romantic chess such as the King's Gambit and Philidor's Defense fell out of use among elite players, while the Queen's Gambit, previously rare, became a staple of high-level chess. By the opening years of the 20th century, chess masters outside of Europe began to appear (previously, Paul Morphy had been the only notable non-European player). These included the Americans Harry Nelson Pillsbury and Frank Marshall, and later the Cuban Jose Raul Capablanca. Emanuel Lasker held onto the world championship a record 27 years, although he did not play chess for long periods of time owing to his career as a mathematics professor. Hypermodern school The hypermodern school was founded by Aron Nimzowitsch, Richard Réti, Savielly Tartakower, Gyula Breyer, and Ernst Grünfeld in the 1920s . The hypermodernists rejected the idea that occupation of the center was important. Instead, the hypermodern school emphasizes control of the center by attacking it with pieces – especially from the periphery. The hypermodern school also denied the superiority of the in all types of positions and claimed that the bishop pair was only strong in open or semi-open positions . While e4 openings and tactical play were still common during the classical era, the post-WWI period saw a significant shift as e4 openings of any kind became unfashionable outside the amateur level. Richard Reti went so far as to pronounce e4 "a decisive mistake" and argued that d4 was the only rational way to open a game, while the Sicilian and French Defense were the only rational responses to 1. e4. Players such as Frank Marshall and Jose Raul Capablanca (who took the world championship from Lasker in 1921), formerly known as tactical players and users of e4 openings, began switching their repertoires to queen side pawn openings and a more positional style of play in the 1920s. In 1927, Alexander Alekhine challenged Capablanca for the world championship. The match, lasting 34 games, was held in Buenos Aires, Argentina and achieved infamy for its overuse of the Orthodox Defense of the Queen's Gambit Declined, which was used in all but two games (the remaining two featured a French Defense and Queen's Indian Defense). Alekhine defeated Capablanca to become the fourth world chess champion, which he retained until his death in 1946 (aside from two years where he lost the title to Max Euwe). The excessive use of the Queen's Gambit Declined Orthodox Defense in