The Polish-Soviet War of 1919-1921 was a direct consequence of the ideological objectives pursued by the belligerents. Ideology shaped the political agenda and the diametrically opposed war aims of both states, and was implemented through the foreign policy, diplomatic negotiation and military engagements pursued. This proved to be the principal obstacle to the establishment of cordial relations. As western democracy and Russian Marxism battled it out, war was inevitable. Externally, the Paris Peace Conference provided the necessary conditions for the resumption of traditional Russian-Polish hostilities, whilst the Allied States consistently demonstrated their absolute inability to directly influence either the development, or outcome, of the conflict.Redressing the balance of historiography, this thesis includes a greater examination of the conflict from the perspective of the Soviet regime. This firmly controlled the Russian decision-making process. By charting the war, it becomes clear that both states deliberately pursued a dual offensive: traditional diplomatic negotiation and military campaign as conditions dictated. However, in addition, Soviet Russia developed a unique and innovative, revolutionary, agit-prop, diplomatic medium. This enabled adept Soviet diplomats to win the majority of diplomatic battles during the conflict, although often negotiating from a militarily weak position.Nevertheless, the regime ultimately failed in its objective: to ignite socialist revolution in western Europe. The mistaken Soviet decision in July 1920 to cross the ethnographic border to forcefully sovietise Poland, in opposition to Marxist doctrine, irreversibly altered the complexion of the war and proved its pivotal turning point. This culminated politically with the short-lived establishment of the Provisional Revolutionary Committee in Białystok, and militarily, with the decisive defeat of the Red Army at the Battle of Warsaw. It is now certain that the Red Army offensive into Poland in July 1920 aimed not only at the sovietisation of Poland, but at spreading the socialist revolution to Western Europe and overthrowing the Versailles settlement. The European revolutionary upsurge had largely extinguished during the previous year and in August 1920, Communist ideology ultimately failed to inspire the vast majority of the Polish population. Thus, by utilising the Soviet military to secure its war aims, Lenin and the Politburo inadvertently signed the death-warrant of socialist revolution in Poland at the beginning of the twentieth century.