Complex sentence: On April 15,1972 he declared state of "internal war" which suspended civil liberties and was then extended by National Assembly in September 1972, November 1972 and March 1973.
Split into simpler sentences: On April 15,1972, he declared a state of "internal war" and suspended civil liberties. That was then extended by the National Assembly in September 1972, November 1972, and March 1973.