Complex sentence: Between December 31,1910, and December 1,1921, Istria lost 15.1% of its population--the last survey under the Austrian empire recorded 404,309 inhabitants, which were reduced to 343,401 by the first Italian census after the war.
Split into simpler sentences: Between December 31,1910, and December 1,1921, Istria lost 15.1% of its population. The last survey under the Austrian empire recorded 404,309 inhabitants, which dropped to 343,401 by the first Italian census after the war.