One of the causes of the Thirty Years' War (1618-1648) was the growing religious and political tension between Roman Catholics and Protestant Christians. The effects of the war included the creation of the Peace of Westphalia and a start to remaking the religious and political boundaries in Europe.
Holy Roman Emperor Ferdinand II, a Catholic, began to interfere with the practice of Protestant Christianity by his subjects. The Protestants, in turn, sought aid from Protestant nations such as Great Britain, Denmark and the Dutch Republic. This move prompted Ferdinand to seek help from Catholic countries, such as those under the papacy, as well as Spain and the Catholic population of Germany. After several early victories, the Catholic side eventually ran into fierce resistance from King Gustavus Aldophus of Protestant Sweden.
After the two sides had each scored varying amounts of success, the Peace of Westphalia created a tentative, if not quite harmonious, peace between the warring factions. Some historians see the end of the war as an end to the wars of religion which had formerly shook the continent. The peace also eventually paved the way for the creation of truly individual nations in Europe. On a darker note, the war had decimated a good portion of the European population.