The first was the need to rebuild Lisbon after a disastrous fire and earthquake in 1755, second was the financial drain of massive military expenditures for the wars with Spain in the 1760's and 70's over the border of southern Brazil. Finally, the gradual exhaustion of Brazilian mines was becoming a problem, gold and diamond revenues from Minas Gerais dropped by 50% in the years between 1750 -1770.
Pombal was a mercantilist and believed that as a good mercantilist Portgual should industrialize while leaving the colonies to produce primary goods for export to the main country. To be sure the Brazil would continue to produce primary goods Pombal did two things: he ordered a complete overhaul of Brazil's economic administrative structure, this meant subjugating all Brazilian law and practice to reinterpretation by jurists who were sympathetic to mercantilist views of a colony's function, and second, he encouraged the creation of three monopoly trading companies between 1755-65. The monopolies were to exploit exports from Amazonia, Pernambuco region, and the coastal whaling industry. During all this, Pombal encouraged the creation of industry at home in Portugal.
Pombal's efforts were very beneficial to Portugal. Sugar production was recovered, wheat cultivation was successfully introduced, and rice and indigo exports were increased. All this helped to reduce Portugal's trade deficit by about 70% between 1751 - 1775. This economic trend continued even after Pombal's fall in 1777. By the year 1800, the colony's exports were thriving, and was aided especially by a revolt in Hiati which disrupted the competing Caribbean sugar trade. By 1807 Portugal was showing healthy surplus in its trade balance and was even with England. Portugal's success however is not the main point to be evaluated, Pombal's aggressive mercantilist intervention in Luso-Brazilian policy meant that Brazil was being left out on the most important development of the era, the industrial revolution.