Mexican president Porfirio Díaz brought unprecedented economic growth during the last quarter of the nineteenth century. This growth was accompanied by foreign investment and European immigration, the development of an efficient railroad network and the exploitation of the country's natural resources. Annual economic growth between 1876 and 1910 averaged 3.3%. Political repression and fraud, as well as huge income inequalities exacerbated by the land distribution system based on latifundios, in which large haciendas were owned by a few but worked by millions of underpaid peasants living in precarious conditions, led to the Mexican Revolution (1910–1917), an armed conflict that drastically transformed Mexico's political, social, cultural, and economical structure during the twentieth century under a premise of social democracy. The war itself, however, left a harsh toll in the economy and population, which decreased over the 11-year period between 1910 and 1921. The reconstruction of the country was to take place in the following decades. The period from 1930 to 1970 was dubbed by economic historians as the "Mexican Miracle", a period of economic growth spurred by a model of import substitution industrialization (ISI) which protected and promoted the development of national industries. Through the ISI model, the country experienced an economic boom through which industries rapidly expanded their production. Important changes in the economic structure included free land distribution to peasants under the concept of ejido, the nationalization of the oil and railroad companies, the introduction of social rights into the constitution, the birth of large and influential labor unions, and the upgrading of infrastructure. While population doubled from 1940 to 1970, GDP increased sixfold. The ISI model had reached its peaked in the late 1960s. During the 1970s, the administrations of Echeverría and López Portillo, tried to include social development in their policies, an effort that entailed more public spending. With the discovery of vast oil fields in a time in which oil prices were surging and international interest rates were low -and even negative- the government decided to borrow from international capital markets to invest in the state-owned oil company, which in turn seemed to provide a long-run income source to promote social welfare. In fact, this method produced a remarkable growth in public expenditure, and president López Portillo announced that the time had come to learn to "manage prosperity" as Mexico multiplied its oil production to become the world's fourth largest exporter. In the period of 1981–1982 the international panorama changed abruptly: oil prices plunged and interest rates rose. In 1982, president López Portillo, just before ending his administration, suspended payments of foreign debt, devalued the peso and nationalized the banking system, along with many other industries that were severely affected by the crisis, among them the steel industry. While import substitution had produced an era of industrialization in previous decades, by the 1980s it was evident that that protracted protection had produced an uncompetitive industrial sector with low productivity gains. President de la Madrid was the first of a series of presidents that began to implement neoliberal reforms. After the crisis of 1982, lenders were unwilling to return to Mexico and, in order to keep the current account in balance, the government resorted to currency devaluations, which in turn sparked unprecedented inflation, which reached a historic high in 1987 at 159.7%. The first step toward the liberalization of trade was Mexico's signature of the General Agreement on Tariffs and Trade (GATT) in 1986. During the Salinas administration many state-owned companies were privatized. In 1992, the North American Free Trade Agreement was signed between the United States, Canada and Mexico, and after the signature of two additional supplements on environments and labor standards, it came into effect on January 1, 1994. Salinas also introduced strict price controls and negotiated smaller minimum wage increments with labor unions with the aim of curbing inflation. While his strategy was successful in reducing inflation, growth averaged only 2.8 percent a year. Moreover, by fixing the exchange rate, the peso became rapidly overvalued while consumer spending increased, causing the current account deficit to reach 7% of GDP in 1994. The deficit was financed through tesobonos a type of public debt instrument that reassured payment in dollars. The Chiapas uprising, and the assassinations of the ruling party's presidential candidate, Luis Donaldo Colosio and the Secretary-General of the party and brother of the Assistant-Attorney General José Francisco Ruiz Massieu in 1994, sent a disquieting message to investors. Public debt holders rapidly sold their tesobonos, depleting the Central Bank's reserves, while portfolio investments, which had made up 90% of total investment flows, left the country as fast as they had come in. This unsustainable situation eventually forced the entrant Zedillo administration to abandon the fixed exchange rate. The peso sharply devalued and the country entered into an economic crisis in December 1994. The boom in exports, as well as an international rescue package crafted by American president Bill Clinton, helped cushion the crisis. In less than 18 months, the economy was growing again, and annual rate growth averaged 5.1 percent between 1995 and 2000. President Zedillo and president Fox continued with trade liberalization and during his administrations several FTAs were signed with Latin American and European countries, Japan and Israel, and both strove to maintain macroeconomic stability. Thus, Mexico became one of the most open countries in the world to trade, and the economy base shifted accordingly. Total trade with the United States and Canada tripled, and total exports and imports almost quadrupled between 1991 and 2003. The nature of foreign investment also changed from portfolio to foreign-direct investment (FDI).