. at the beginning of the twentieth century, the mexican revolution led the institutional revolutionary party (pri) to power. every six years, the leaders of this party chose a presidential candidate, and these candidates were always elected by the people. the influence of the pri grew through the 1950s and early 1960s as economic improvements raised wages for many mexicans. by the late 1960s, however, some began to contest the one-party system of government, and a group of students protesting this issue was attacked by police in mexico city in 1968. in response to these concerns, the next two pri presidents encouraged greater freedom of the press and more freedom in universities, and encouraged the existence of other political parties. also during this period, new oil reserves were discovered in mexico, providing new financial resources. after this period of renewed prosperity, however, the pri suffered when oil prices dropped in the 1980s, making it impossible for the government to repay foreign debts and forcing the privatization of many government companies. these economic changes led to rising unemployment, and the mexican people became dissatisfied with the pris leadership once again. in 2000, vicente fox defeated the pri candidate and became president of mexico, the first president not associated with the pri since the mexican revolution.