Remember not every word you use will be identtified as a "subject" by your search tool. This is especially true with the words: International, World, and Global. Concentrate on the subject terms and then look for keywords that indicate that your results will cover a global perspective.
HINT: Often signed encyclopedia or handbook articles (references sources) are written by experts who have written other texts (books, articles, blog posts, etc.) You can search for those authors in CLICsearch or Google to discover some of their other works. Reference sources often also have a Further Reading section or a Bibliography at the end of them, with other sources on your topic, that can be worth exploring.