Chapter 5 investigates the League of Landsberg’s failed attempt to admit new Protestant and Catholic territories in the early 1570s, including the Low Countries. The League’s proposed expansion presented an opportunity to create a lasting peace in the Empire by forging new ties among competing territories. At multiple points, however, both Catholics and Protestants rejected this possibility, as neither party wished to cede primary authority in the alliance. Even as the League continued to resolve neighborly disputes, support for its exercise of shared sovereignty eroded. Related processes operated in the Low Countries during the 1570s, where civil war spawned competing alliances: the Union of Arras and the Union of Utrecht. Including members that supported a variety of religious policies, the Union of Utrecht tried to solve the problem of religious diversity by devolving authority over religion to provincial governments. Such a solution meant that much of the United Provinces’ subsequent political development depended on how different provincial authorities interpreted the meaning of the Union’s treaty of alliance. This dynamic remained at the heart of the Dutch Republic and its exercise of shared sovereignty throughout the late sixteenth and seventeenth centuries.