Complex sentence: Despite the exodus of Slovene and German speakers, the population in the city increased due to internal migration of Italians from other parts of Italy; furthermore, several thousand ethnic Italians from Dalmatia moved to Trieste from the newly created Yugoslavia.
Split into simpler sentences: Despite the exodus of the Slovene and German speakers, the city's population increased because of the migration of Italians from other parts of Italy. Several thousand ethnic Italians from Dalmatia also moved to Trieste from the newly created Yugoslavia.