Treaty of Westphalia
The Thirty Years War was a political and religious war that devastated the Holy Roman Empire of the German nation in the 17th century. First a religious conflict between the Protestant princes and the Catholic house of Hapsburg, it degenerated into a European war due to the intervention of the foreign powers, Sweden and France. The Treaty of Westphalia put an end to it in 1648, mainly to the benefit of Sweden and France.
Article : The Thirty Year War (1618-1648)