Complex sentence: During 14th and 15th century population of the region and merchants from Dubrovnik used Ostrovica castle as a haven during wars, for the first time in 1323--1324 during the war between Stefan Dečanski and Stephen Vladislav.
Split into simpler sentences: During 14th and 15th century population of the region and merchants from Dubrovnik used Ostrovica castle as haven during wars. It was used as haven for the first time in 1323--1324 during the war between Stefan Dečanski and Stephen Vladislav.