Complex sentence: Region had been occupied by Romanian army amid breakup of the Russian Empire in 1918 and, between 1918 and 1940, Izmail once again became, with the rest of Bessarabia, part of the Kingdom of Romania.
Split into simpler sentences: Region had been occupied by Romanian army amid breakup of the Russian Empire in 1918. Between 1918 and 1940, Izmail was, with the rest of Bessarabia, part of the Kingdom of Romania.