Two very cold winters near the end of the Little Ice Age led directly to a famine between 1740 and 1741, which killed about 400,000 people and caused over 150,000 Irish to leave the island. In addition, Irish exports were reduced by the Navigation Acts from the 1660s, which placed tariffs on Irish products entering England, but exempted English goods from tariffs on entering Ireland. Despite this most of the 18th century was relatively peaceful in comparison with the preceding two centuries, and the population doubled to over four million.