Modern nation-states did not exist in their present form until 1648 (Treaty of Westphalia), and the state's monopoly on warfare, or inter-state violence, is even more recent. The lack of central governments made it impossible to use terror as a method of affecting a political change, as there was no single dominant political authority. Also, the absence of central authority meant that the game of warfare was open to many more players. Instead of national armies, a variety of non-sovereign nobility, mercenaries, leaders of religious factions, or mercantile companies participated in warfare. Their involvement in warfare was considered to be perfectly legitimate. This is in contrast to the modern era, where nations go to war, but private participation is actually illegal.