Immigration to America has occurred in waves throughout history. During the colonial era, most immigrants came from northern Europe, but this declined during the Revolutionary War. Immigration increased strongly again in the 1840s-1850s, with most newcomers originating from Ireland and Germany fleeing famine and crop failures. By the 1860s, over half of New York City's population was immigrants or their American-born children. After the Civil War, America's growing economy attracted many European workers between 1866-1915, initially from northern Europe but later mostly from southern and eastern Europe. Reaction to events like the Russian Revolution led to immigration quotas and restrictions in the 1920s based on national origin. Immigration declined during World War I, the 1920s, and 1930