Willem Mengelberg
Vermeulen's dissatisfaction with the artistic policies of the Royal Concertgebouw Orchestra and its leader Willem Mengelberg came to a head in November 1918. After a performance of the Seventh Symphony of Cornelis Dopper, conducted by the composer, Vermeulen stood up and shouted "Long live Sousa!" from the stands of the Concertgebouw. A part of the audience thought that the socialist leader Troelstra, who had attempted a revolution days earlier, was meant and therefore interpreted Vermeulen's words as incitement, leading to great turmoil and a flurry of publications. The orchestra considered whether or not they could ban specific journalists from the hall. The incident also highlighted the already lumbering conflict between traditionalists (represented by Cornelis Dopper and chief conductor Willem Mengelberg) and avant-garde figures such as assistant conductor Evert Cornelis.