After the secession of Southern states began in 1861, the Missouri legislature called for the election of a special convention on secession. Pro-Southern Governor Claiborne F. Jackson ordered the mobilization of several hundred members of the state militia who had gathered in a camp in St. Louis for training. Alarmed at this action, Union General Nathaniel Lyon struck first, encircling the camp and forcing the state troops to surrender. Lyon directed his soldiers, largely non-English-speaking German immigrants, to march the prisoners through the streets, and they opened fire on the largely hostile crowds of civilians who gathered around them. Soldiers killed unarmed prisoners as well as men, women, and children of St. Louis in the incident that became known as the "St. Louis Massacre".