Czechoslovak interests were subordinated to the interests of the Soviet Union. Joseph Stalin became particularly concerned about controlling and integrating the socialist bloc in the wake of Tito's challenge to his authority. Stalin's paranoia resulted in a campaign against "rootless cosmopolitans" which culminated in the conspiracy theory of the alleged Doctors' plot. In Czechoslovakia, the Stalinists also accused their opponents of "conspiracy against the people's democratic order" and "high treason" in order to oust them from positions of power. Many Communists with an "international" background, i.e., those with a wartime connection with the West, veterans of the Spanish Civil War, Jews, and Slovak "bourgeois nationalists", were arrested and executed in show trials (e.g., Heliodor Píka, Milada Horáková). Most spectacular was the Slánský trial against KSČ first secretary Rudolf Slánský and thirteen other prominent Communist personalities in November and December 1952. Slánský and ten other defendants were executed, while three were sentenced to life imprisonment. The KSČ rank-and-file membership, approximately 2.5 million in March 1948, began to be subjected to careful scrutiny. By 1960, KSČ membership had been reduced to 1.4 million.