The Knights of Labor was the United States’ first sizeable organization of workers united for the purpose of advocacy; in the 1880s the group had between 700,000 and 800,000 members, about a tenth of the nation’s industrial workforce. The Knights called for an eight-hour working day, the abolition of child labor, and better pay. The most unusual aspect of the Knights was the nature of its membership. Any worker could join, male or female, of any skill level, and even of any race, although the Knights supported bans on immigration. After the Haymarket Affair in 1886, in which seven policemen were killed in a bombing at a Chicago labor demonstration, membership declined precipitously—but the decline also opened up opportunities for diversity in the organization’s leadership.