Complex sentence: Before any true peacekeeping mission United Nation played an important role in the conflict concerning Trieste from 1947 to 1954, Trieste was declared an independent city state under the protection of the United Nations as the Free Territory of Trieste.
Split into simpler sentences: Before any true peacekeeping mission United Nation played an important role in the conflict concerning Trieste. From 1947 to 1954, Trieste was declared an independent city state under the protection of the United Nations as the Free Territory of Trieste.