Mexico's inward-looking development strategy produced sustained economic growth of 3 to 4 percent and modest 3 percent inflation annually from the 1940s until the 1970s. This growth was sustained by the government's increasing commitment to primary education for the general population from the late 1920s through the 1940s. The enrollment rates of the country's youth increased threefold during this period; consequently when this generation was employed by the 1940s their economic output was more productive. Additionally, the government fostered the development of consumer goods industries directed toward domestic markets by imposing high protective tariffs and other barriers to imports. The share of imports subject to licensing requirements rose from 28 percent in 1956 to an average of more than 60 percent during the 1960s and about 70 percent in the 1970s. Industry accounted for 22 percent of total output in 1950, 24 percent in 1960, and 29 percent in 1970. The share of total output arising from agriculture and other primary activities declined during the same period, while services stayed constant. The government promoted industrial expansion through public investment in agricultural, energy, and transportation infrastructure. Cities grew rapidly during these years, reflecting the shift of employment from agriculture to industry and services. The urban population increased at a high rate after 1940 (see Urban Society, ch. 2).