Many Irish who fled their homeland because of the Great Famine of the 1840s (over one million people died as a result of this famine) immigrated to the United States. A significant number of them went to Puerto Rico after being turned away at American ports because of epidemic outbreaks on board the ships on which they sailed. Many of these Irish settlers were instrumental in the development of the island's hugely successful sugar industry. This industry was vital to the growing local economy.