Complex sentence: Prior to the 1840s, few Chinese emigrated to the United States or Canada, although large numbers had left China, particularly Fujian and Canton, since the seventeenth century to seek their fortune in southeast Asia and Taiwan.
Split into simpler sentences: Prior to the 1840s, few Chinese emigrated to the United States or Canada. Large numbers had left China, particularly Fujian and Canton, since the seventeenth century in order to seek their fortune in southeast Asia and Taiwan.