Complex sentence: The Convention on the Territorial Sea and Contiguous Zone of 1958 is an international treaty, one of four agreed upon at the first United Nations Convention on the Law of the Sea (UNCLOS I).
Split into simpler sentences: The Convention on the Territorial Sea and Contiguous Zone of 1958 is an international treaty. The treaty was one of four agreed upon at the first United Nations Convention on the Law of the Sea (UNCLOS I).