After the death of Martin Luther in 1546, the Schmalkaldic War started out as a conflict between two German Lutheran rulers in 1547. Soon, Holy Roman Imperial forces joined the battle and conquered the members of the Schmalkaldic League, oppressing and exiling many German Lutherans as they enforced the terms of the Augsburg Interim. Religious freedom was secured for Lutherans through the Peace of Passau in 1552, and under the Cuius regio, eius religio  and Declaratio Ferdinandei  clauses of the Peace of Augsburg in 1555. Religious disputes between the Crypto-Calvinists, Philippists, Sacramentarians, Ubiquitarians and Gnesio-Lutherans raged within Lutheranism during the middle of the 16th century. This finally ended with the resolution of the issues in the Formula of Concord. Large numbers of politically and religiously influential leaders met together, debated, and resolved these topics on the basis of Scripture, resulting in the Formula, which over 8,000 leaders signed. The Book of Concord replaced earlier, incomplete collections of doctrine, unifying all German Lutherans with identical doctrine and beginning the period of Lutheran Orthodoxy.

How many years after the death of Martin Luther did the Schmalkaldic War start out as a conflict between two German Lutheran rulers?
1