As a diplomat, Christian played an important role in the formation of the Protestant Union in 1608. With the death of the Elector Frederick IV, Christian served his son, Frederick V, and was appointed to command the Protestant forces to defend Bohemia against Holy Roman Emperor Ferdinand II and his allies when that country's nobles elected Frederick as their king in 1619. The same year, Christian was accepted in the Fruitbearing Society. When Bohemian forces were defeated at the Battle of White Mountain in 1620, Christian advised Frederick against making a stand in Prague. In 1621, in response to his affiliation with the Palatines, Christian was put under an imperial ban that effectively made him an outlaw within the Holy Roman Empire and stripped him of his lands.