In 1552 Julius' father Duke Henry V had joined a princely alliance against the not less warlike Hohenzollern margrave Albert Alcibiades of Brandenburg-Kulmbach. During the Second Margrave War, both sides met in the 1553 Battle of Sievershausen, where both Julius' elder brothers were killed in action. Suddenly, he became heir to the principality – for the distress of his father, who noted his feeble constitution and his sympathies for French culture and the Protestant faith. Julius avoided an open conclict and temporarily withdrew to his residence at Hessen Castle. As all plans to exclude him from the line of succession had failed, he succeeded as ruling Prince of Brunswick-Wolfenbüttel upon his father's death in 1568. He moved to Wolfenbüttel Castle.