Question: Which territory did Roman von Ungern-Sternberg's forces and the Transbaikal fight over? 
Sentence (from "Roman von Ungern-Sternberg"): Baron Roman Nicolaus Maximilian von Ungern-Sternberg (Russian: Барон Ро́берт-Ни́колай-Максими́лиан Рома́н Фёдорович фон У́нгерн-Ште́рнберг ) (10 January 1886 NS – 15 September 1921) was an anti-Bolshevik lieutenant general in the Russian Civil War and then an independent warlord whose Asiatic Cavalry Division wrested control of Mongolia from the Republic of China in 1921 after its occupation.
Relevant evidence: Yes