Andover was instrumental in preparing the first Congregational missionaries for overseas mission. The churches already had sent missionaries to frontier America. The American overseas missionary movement had its informal beginning in 1806 when Samuel J. Mills met with four fellow students at Williams College in Massachusetts for a Sunday afternoon prayer meeting in a maple grove. A sudden thunderstorm drove them to the shelter of a haystack where, surrounded by thunder and lightning, Mills proposed a mission to preach the Gospel in Asia. His zeal ignited the four others with the intent "to evangelize the world," and they went on to study theology at Andover Seminary.
One of them, Adoniram Judson, who later joined the Baptist churches, had appealed to the London Missionary Society for support but was rejected. Believing it was time for American Congregationalism to support its own missionaries, the Andover faculty and leaders of the Massachusetts General Association authorized a cooperative missionary venture by the churches of Massachusetts and Connecticut. On September 5, 1810, the American Board of Commissioners for Foreign Missions was born—the first foreign missionary society in the United States. On February 8, 1812, at a moving service of worship in the crowded Salem Tabernacle Church, the Haystack "Brethren" were ordained. Within two weeks, they set sail for India.
In the same year, New England Congregational clergy voted to condemn the War of 1812 as "unnecessary, unjust, and inexpedient." Their antiwar sermons and political organizing in opposition to a government policy were unprecedented.
The American Board of Commissioners for Foreign Missions intended to establish missions not only in the Orient and Burma, but also "in the West among the Iroquois." Subsequently, throughout the 1820s and 1830s missions were organized among the Creek, Choctaw, Chickasaw and Cherokee, Osage, Maumee and Iroquois. In an effort supported by Congregationalists and members of other churches, the American Board provided aid for Indian resistance to government removal from their lands.

Backs Cherokee sovereignty

In a celebrated case, the American Board supported the Rev. Samuel A. Worcester, missionary to the Cherokee, in his lawsuit before the United States Supreme Court to prevent the state government of Georgia from deporting the Cherokee nation from territory recognized as sovereign under United States law. The court ruled in favor of the Cherokees, finding that the Cherokee nation were under United States protection and could not be expelled from their land. But President Andrew Jackson ignored the court and ordered the tribes removed anyway. They were forced to move westward without adequate provision or shelter; many died on the way.
The German Reformed Church was also active in missions—both among Native Americans and recent German immigrants. More than 300 churches were built. Swiss and German students from Mercersburg Theological Seminary aided Germans on the western rontier. In 1862, the Sheboygan Classis of the German Reformed Wisconsin Synod founded Mission House to train local men as ministers and teachers. It initiated a ministry among American Indians in the 1870s by an act of providence. Professor H. Kurtz, overtaken by a snowstorm, succumbed to fatigue on a 12-mile return walk from a Sunday preaching mission. Some Winnebagos, finding him asleep in the snow, took him back to Mission House. Kurtz promoted help for Indians of the area, and in 1876, the Classis declared, "As soon as we have the money to find a missionary, we will send him to the Indians who live nearest us." The Classis sent Jacob Hauser to the Winnebagos in 1878. He was warily received, but interest in their children's education and belief that all people shared one God, the Earthmaker, helped smooth relations between the missionary and the community. Twenty years later a church was started. The Winnebago Indian School at Neillsville, Wisconsin was founded in 1917. It trained Christian ministers, teachers, nurses and leaders for the Winnebago people, among them Mitchell Whiterabbit, a pastor who later became a national leader in the United Church of Christ.