In 1944, after various incidents, including one in which he declined to greet the Nazi Reichsprotektor Karl Hermann Frank with a Hitler salute, along with his refusal to conduct Wagner during the War, Kubelík "deemed it advisable to disappear from Prague and to spend a few months undercover in the countryside so as not to fall into the clutches of the SS or Gestapo". Kubelík conducted the orchestra's first post-war concert in May 1945. In 1946, he helped found the Prague Spring Festival, and conducted its opening concert. After the Communist coup of February 1948, Kubelík left Czechoslovakia, vowing not to return until the country was liberated. "I had lived through one form of bestial tyranny, Nazism," he told an interviewer, "As a matter of principle I was not going to live through another." He defected during a trip to Britain, where he had flown to conduct Mozart's "Don Giovanni" with the Glyndebourne company at the Edinburgh Festival. He had been engaged on the recommendation of Bruno Walter, whom Kubelík had assisted in this work at the 1937 Salzburg Festival. Kubelík told his wife of his decision to defect as their plane left Czechoslovakia. In 1953, the Communist government convicted the couple "in absentia" of "taking illicit leave" abroad. In 1956, the regime invited him back "with promises of freedom to do anything I wanted," said Kubelík, but he refused the invitation. In a 1957 letter to "The Times", Kubelík said he would seriously consider returning only when all the country's political prisoners were freed and all émigrés were given as much freedom as he would have possessed. He was invited back by the regime in 1966 but again refused; in 1968, after the Prague Spring had been ended by the Soviet invasion, he organised an international boycott, in which many of the major classical artists of the West participated. In 1950, Kubelík became music director of the Chicago Symphony Orchestra, choosing the position over an offer from the BBC to succeed Sir Adrian Boult as chief conductor of the BBC Symphony Orchestra. He left the post in 1953. Some hold that he was "hounded out of the [Chicago] job" (to quote "Time magazine") by the "savage attacks" (to quote the New Grove Dictionary of Music and Musicians) of the "Chicago Tribune" music critic Claudia Cassidy. But "Chicago Sun-Times" music critic Robert C. Marsh argued in 1972 that it was the Chicago Symphony trustees who were behind the departure.