The armistice of Belgrade signed on 13 November 1918 defined a demarcation line marking the southern limit of deployment of most Hungarian armed forces.

The terms of the armistice and the subsequent actions of the Allies embittered a significant part of Hungary's population and caused the downfall of the First Hungarian Republic, which had been established only days after its signing.

During the war, the Hungarian communists fought separate battles against troops from Czechoslovakia and Romania, and France was also highly involved[4] diplomatically in the conflicts.

The Hungarian government, claiming to impose the will of the Allies on Romania and seeing that it would not be compelled by diplomatic solutions, resolved to clear the threat by military force once and for all.

[5][6][7] See also 1918 occupation of Međimurje and Creation of Yugoslavia Shortly after the Kingdom of Serbia was liberated, the new Banat republic was proclaimed on 1 November, but it was not able to achieve control over most of the territory it claimed; the Belgrade Agreement of 15 November 1918 and previous Allied promises had mandated Serbian control, and the Serbian army entered western and central parts of Banat (including Temeschwar) and abolished the republic; the Romanian army entered the eastern part of the region.

The Treaty of Trianon assigned most of the Baranja region to Hungary, which led to massive protests and to a group of people, under the painter Petar Dobrović, to proclaim a Serb-Hungarian Baranya-Baja Republic.

In the name of what they considered to be war reparations, the Romanian government requested the delivery of 50% of the country's rolling stock, 30% of its livestock and 20,000 carloads of fodder and even assessed payment for their expenditures.

By early 1920, it had seized much from Hungary, including food, trucks, locomotives and railroad cars, factory equipment and even the telephones and typewriters from government offices;[8] the Hungarians regarded the Romanian seizures as looting.