 A series of invasions in the earlier half of the Joseon caused a dynamic shift in the culture during the second half of the period.Groups of "silhak" ("practical learning") scholars began to emphasize the importance of looking outside the country for innovation and technology to help improve the agricultural systems.Crops traded by Europeans from the New World began to appear, acquired through trade with China, Japan, Europe, and the Philippines; these crops included corn, sweet potatoes, chili peppers, tomatoes, peanuts, and squash.