The Soviet conquest of Poland was one of the preliminary objectives in the Soviet attempt to establish communist control over all Europe. The Soviets' ambition to achieve a communist Europe is as old as the existence of the Soviet Union. The first attempt to conquer Poland, which stood on their way to Western Europe, had failed in 1920. That bitter experience convinced the rulers in the Kremlin that revolutionary forces in Poland were not powerful enough to fulfill what their orthodox Marxism taught them to be "historically inevitable." By signing the Treaty of Riga in 1921, which ended the Soviet-Polish War, the Soviet Union not only repudiated the Curzon Line as an "unjust frontier" to Poland but publicly stated that the Riga Treaty was more beneficial to the Soviet Union than to Poland. After the signing of the Soviet-Polish Treaty of 1941, the Soviets never implemented its terms.