Task: Question Generation
Input (English): According to the preamble in The Law of Treaties, treaties are a source of international law. If an act or lack thereof is condemned under international law, the act will not assume international legality even if approved by internal law. This means that in case of a conflict with domestic law, international law will always prevail.
Output (English): What are started to be a source of international law in the preamble in The Law of Treaties?