be held and a permanent constitutional system established. The communists' principal rivals were veteran activists of the Polish Underground State, Mikołajczyk's Polish People's Party (Polskie Stronnictwo Ludowe, PSL), and veterans of the Polish Armed Forces in the West. Of particular practical importance was Mikołajczyk's People's Party (originally a peasant formation), because it was legally recognized by the communists and thus able to function within the political arena. The People's Party wanted to prevent the communists from monopolizing power and eventually establish a parliamentary polity with a market economy by winning the promised elections. Mikołajczyk hoped that an independent Polish state, friendly with the Soviet Union, would be allowed to act as a bridge between the East and the West. Soviet-oriented parties, backed by the Soviet Red Army and in control of the security forces, held most of the power, concentrated especially in the Polish Workers' Party under Gomułka and Bierut. Bierut represented the influx of appointees to the Polish party coming (during and after the war) from the Soviet Union and imposed by the Soviets, a process accelerated at the time of the PPR Congress of December 1945. The party's membership dramatically increased from perhaps a few thousand in early 1945 to over one million in 1948. As a show of Soviet domination, sixteen prominent leaders of the Polish anti-Nazi underground were brought to trial in Moscow in June 1945. Their removal from the political scene precluded the possibility of a democratic transition called for by the Yalta agreements. The trial of the defendants, falsely and absurdly accused of collaboration with the Nazis, was watched by British and American diplomats without protest. The absence of the expected death sentences was their relief. The exiled government in London, after Mikołajczyk's resignation led by Tomasz Arciszewski, ceased to be officially recognized by Great Britain and the United States on 5 July 1945. In the years 1945–47, about 500,000 Soviet soldiers were stationed in Poland. Between 1945 and 1948, some 150,000 Poles were imprisoned by the Soviet authorities. Many former Home Army members were apprehended and executed. During the PPR Central Committee Plenum of May 1945, Gomułka complained that the Polish masses regard the Polish communists as the "NKVD's worst agency" and Edward Ochab declared the withdrawal of the Soviet Army from Poland a high priority. But in the meantime tens of thousands of Poles died in the postwar struggle and persecution and