Theater, like all the arts, was used as a tool of propaganda in totalitarian societies such as Nazi Germany and the Soviet Union. Everyone involved in the theater had to be politically reliable; they had to join professional organizations established and controlled by the state. Anyone considered politically suspect would be barred from these organizations and thus unable to make a living in their chosen profession. All plays had to be strictly vetted by the appropriate propaganda department before they were allowed to be produced. Anything that could vaguely be interpreted as departing from the official Party line was censored or removed altogether.
In practice, this meant that creativity practically dried up. As the authorities considered political reliability much more important than talent, theaters of totalitarian societies became crowded with third-rate works by Party hacks chosen solely for their ideological fanaticism. There was no room for experimental or daring works that might challenge the audience to see the world in a different way. Totalitarian regimes only want the people they control to see things from their own perspective; no one else must be allowed to present alternative ideas, and that especially includes artists.
Not all plays had to be overtly political, however. Hitler's propaganda chief Goebbels understood very well that audiences would much rather be entertained than subjected to political messages. As the war progressed, and it became clear that Nazi Germany was heading for defeat, growing numbers of Germans flocked to the theater and the cinema to indulge in escapist entertainment to take their minds off the developing catastrophe.