Soviet Hungarian War with Romania 1919
An incredibly neglected topic in English.
There's a few books on the politics, but I have found nothing at all on the campaign in which Romania crushed the new Soviet Hungary.
Campagnes de larmée roumaine, 1916–1919
I have translated a chapter from Colonel Bujac's book (Paris, Charles Lavauzelle & Cie, 1933) dealing with the Romanian war with Soviet Hungary. It's not particularly long but is densely packed with information. I wouldn't take his word for the politics though – stick to his military stuff.
Bujac Chapter on Romanian Invasion of Hungary 1919
Maps from Bujac – Map A , Map B , Map C
Les armées alliées en Orient après l'armistice de 1918
I have also translated some material from the French official history series relating to this war. There is quite a lot of material, but not particularly even in its coverage. Again, it is provided for military details, not the politics.
Excerpts from Les armées alliées en Orient après larmistice de 1918