 Several empirical studies point to a correlation between the existence of natural resources and the difficulty of turning into a democracy.The first cracks in the system, even though they were merely symbolic, were the 1970s reforms to the electoral system and the composition of the Congress of the Union which for the first time incorporated proportional representation seats allowing opposition parties to obtain seats, though limited in number, in the Chamber of Deputies.As minority parties became involved in the system, they gradually demanded more changes, and a full democratic representation.