Why did Christian IV intervene in the Thirty Years’ War?

King Christian IV of Denmark intervened in the Thirty Years’ War primarily to secure Danish interests and influence in the region. His motivations were twofold:

• Countering Swedish Expansion: Christian IV sought to establish a broad sphere of interest in Germany to serve as a strategic counterweight to the growing influence of Sweden in the Baltic Sea, which he viewed as a threat to Danish control of the area.1
• Supporting Protestantism: As a Protestant monarch, he also wished to strengthen the position of Protestantism within the Holy Roman Empire against the Catholic forces led by the Catholic League and the Habsburgs.12

Ultimately, his military campaign ended in failure following disastrous losses and the occupation of Jutland by Catholic forces, leading Denmark to sign a separate peace treaty in 1629.12