The last three years the Priestleys spent in Britain were a time of political upheaval and the persecution they experienced led to their eventual emigration to the United States. During the Birmingham Riots of 1791, which began on the second anniversary of the storming of the Bastille in the wake of the conservative British reaction against the French revolution, the Priestleys' home, Joseph's church, and the homes of many other religious Dissenters were burned. The Priestleys fled Birmingham and attempted to live in London, but they could not escape the political turmoil. In 1794, they joined the tide of 10,000 emigrants who moved to America—it was the largest emigration from Europe to America until the end of the Napoleonic Wars. The Priestleys left Britain at the beginning of April on the "Samson" and arrived in New York City on June 4, 1794. Two of their three sons, Joseph, Jr. (eldest) and Harry (youngest), had already emigrated to the United States in August 1793, along with Joseph Priestley's friend, the radical activist Thomas Cooper. Their middle son, William, had moved to America from France, probably early in 1793, following the September massacres of the previous year.