I believe they were used to spread Christianity
The philosophy behind it was that of Hobbes, Locke, and Rousseau. They were inspired by works such as the Social Contract when they created the idea that people sovereignty was the highest form of sovereignty and that democracy and the rule of law should be the main thing instead of a monarchy. They part that all men are created equal and should govern themselves is directly taken from books like that one.
It allowed each state to create its own foreign policy.
