The Polish–Romanian alliance was a series of treaties signed in the interwar period by the Second Polish Republic and the Kingdom of Romania. The first of them was signed in 1921 and, together, the treaties formed a basis for good foreign relations between the two countries that lasted until World War II began in 1939.
European context
Immediately after World War I, the peace treaties recognized the reestablishment of a Polish state for the first time in over 100 years. Romania emerged from the war as a victorious nation, enlarging its territory (as Greater Romania). Both states had serious reasons to stand by these treaties.
Having established contacts with Poland in January–February 1919 (after Stanisław Głąbiński's visit to Bucharest), Romania oriented itself towards a cordon sanitaire alliance aimed at Bolshevist Russia and the newly created Comintern; the proclamation of the Hungarian Soviet Republic, the German insurrection, and the Red Army's capture of Odessa alarmed politicians in both countries. The diplomat Czesław Pruszyński reported to the Polish government: "A dam that can put a stop to Bolshevik pressure on the West is constituted of Poland to the north, and Romania to the south. [...] There is a natural necessity, but also a historical necessity, that, based on the mutual interests of Romania and Poland, a military alliance be sealed in front of the common threat facing them."
Romania was not engaged in the Polish-Soviet War, but accepted and supported Polish military transit through its territory. According to another of Pruszyński's reports, Romania facilitated the transit of Polish nationals from Russia to their native areas, as well as furnishing armament and grain at preferential prices. In this context, the Romanian Army intervened in the Polish-Ukrainian War against the West Ukrainian People's Republic (created in Galicia in the summer of that year), helping the Poles in Pokuttya (see Romanian occupation of Pokuttya).
Count Aleksander Skrzyński, acting with the acknowledgement of Polish leaders Ignacy Jan Paderewski and Józef Piłsudski, extended an offer to the Romanian government of Ion I. C. Brătianu to participate in the future administration of Ukraine in its entirety (August 1919); the message was again stated after Skrzyński became ambassador in Romania the following month. Alexandru G. Florescu, the ambassador to Warsaw, reported back that the plan for a common military administration was: "[...] an inaccuracy and a fantasy which I suppose one should not take into account for anything other than making stock of them."
Agreeing with Florescu's assessment, the Brătianu cabinet expressed a will to establish contacts with the Ukrainian People's Republic. In 1920, a similar plan was proposed by Piłsudski himself to the Alexandru Averescu government; the offer was more specific, indicating that Romania was to extend its administration to the east (the Black Sea shore, Odessa, and Transnistria). Averescu refused to accept the proposal, as it meant his country's involvement in the Russian Civil War.
The first treaty
The first treaty was the Convention on Defensive Alliance, signed on March 3, 1921 in Bucharest. The treaty, concluded for a period of five years, committed both parties to rendering armed assistance to one another "in case one of the sides is attacked at its present Eastern frontiers". and was aimed at containing Russia (from 1922, the Soviet Union), which had just lost the Polish-Soviet War. Among the diplomats engaged in negotiations were Polish general Tadeusz Rozwadowski and Romanian general Ion Antonescu. Ratifications for that treaty were exchanged in Bucharest on July 25, 1921. The treaty was registered in League of Nations Treaty Series on October 24 of the same year.
In the early 1920s, Romania, along with Czechoslovakia and Yugoslavia, initiated the Little Entente. The alliance's primary goal was to counter Hungary's revanchism, which involved Romania's Transylvania. Romania's Foreign Minister, Take Ionescu, was unable to bring Poland and Greece into the alliance because of border disagreements between Poland and Czechoslovakia. The Romanian representative in Warsaw reported: "Poland's policy towards the Little Entente [...] becomes clearer. Poland will not wish to join it. [...] This attitude may be related to Mr. Beneš's, who seems to have declared that Poland's joining the treaty is not currently possible."
However, in 1925, the Locarno Treaties were signed in which Germany committed to preserve the status quo in the Rhineland. Germany also signed arbitration conventions with Poland and Czechoslovakia, but the Polish government felt betrayed by France.