Complex sentence: This 1999 Constitution was adopted in December 1999, replacing the 1961 Constitution--which had been, of the 26 constitutions in use by Venezuela since its independence in 1811, the document that had remained in force for the longest time.
Split into simpler sentences: This 1999 Constitution was adopted in December 1999, replacing the 1961 Constitution. The 1961 Constitution which had been, of the 26 constitutions in use by Venezuela since its independence in 1811, the document that has remained in force for the longest time.