Your Topic should not:

• cover a broad and general field of law or
• cover a broad and general idea

It can, however, be your starting point in finding a topic. Read e.g. the latest issues of:
Some general journals on International Law or European Law and/or
a newspaper/blog on International Law or European Law

A Broad and General Idea should be narrowed down

• In what way is my topic problematic? (exploration)
• Why do I want to research this topic? (relevance)
• What do I leave out of my research? (restrict)