During the late Yuan and early Ming, the sparsely-inhabited shoals of the area began to fill with migrants from Pudong and other areas of Songjiang Prefecture. These immigrants introduced cotton cultivation, which spread widely prior to China's opening to international trade in the later Qing. There was small-scale textile production in the area, but most was exported for use in Songjiang, Hangzhou, and other more developed areas of Jiangnan. In the 2nd year of Hongwu (1396) under the Ming, the prefecture was elevated to a county but, shortly afterwards, a major subsidence provoked a mass emigration back to the mainland. This county was later placed in Suzhou and then Taicang Prefectures. The unification of over 30 shoals in 1681 was effectively the creation of the present-day Chongming, although it remained much smaller at the time.