Roman universalism was characterised by cultural and religious tolerance and a focus on civil efficiency and the rule of law. Roman law was imposed on both Roman citizens and colonial subjects. Although Imperial Rome had no public education, Latin spread through its use in government and trade. Roman law prohibited local leaders to wage war between themselves, which was responsible for the 200 year long Pax Romana, at the time the longest period of peace in history. The Roman Empire was tolerant of diverse cultures and religious practises, even allowing them on a few occasions to threaten Roman authority.