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.