By emphasizing the industrial sector, Seoul's export-oriented development strategy left the rural sector relatively underdeveloped. The steel and shipbuilding industries in particular played crucial roles in developing South Korea's economy during this time. Except for mining, most industries were located in the urban areas of the northwest and southeast. Heavy industries generally were located in the south of the country. Factories in Seoul contributed over 25 percent of all manufacturing value-added in 1978; taken together with factories in surrounding Gyeonggi Province, factories in the Seoul area produced 46 percent of all manufacturing that year. Factories in Seoul and Gyeonggi Province employed 48 percent of the nation's 2.1 million factory workers. Increasing income disparity between the industrial and agricultural sectors became a serious problem by the 1970s and remained a problem, despite government efforts to raise farm income and improve rural living standards.