CEVAP:

There were further improvements in diplomatic practices during the 17th century, such as diplomatic immunity and equal treatment for the ambassadors as they were representing the monarchs who were equals in theory, if not in practice. When the Thirty Years’ War ended with the Treaty of Westphalia in 1648, it contained two major principles of diplomacy and the following international system that survived up until the 21st century: Sovereign equality of all states and non-interference to domestic politics of each other.