In the 16th-century, the Protestant Reformation prompted people to challenge Church doctrine, leading to the development of secular movements that challenged the Roman Catholic Church and the papal authority. Soon Europe became divided by religious beliefs, leading to warfare within most countries. Such is the case of the Thirty Years’ War that decimated Europe.
The leage of nations was the predecessor the UN. The UN basically wanted to promote piece in thw world, and mediate small scale conflicts between countries to prevent war
