In the United States, by the middle of the 19th century, the General Synod, then the largest fellowship of Lutheran congregations, was at war with itself over whether or not to allow the changes seen in American Protestantism take hold in Lutheran congregations. In 1855 Rev. Samuel Schmucker anonymously published his “Definite Platform in which he sought to end the influence of confessional Lutheranism in favor of what was termed “American Lutheranism”. But to do this it was necessary to unhinge the General Synod from the Book of Concord, especially the cornerstone document, the Augsburg Confession.
While the Definite Platform was ultimately not adopted, there were enough unionizing efforts among the Lutherans that it became common for a confessional Lutheran congregations to use the designation U.A.C. as part of its name.