If a topic you might consider working on is controversial (for example, the article on Microcredit/Microfinance or Female Genital Mutilation), Wikipedia may restrict changes to the site or others may quickly reverse your changes. Highly trafficked pages may be changed by other users frequently, leaving it difficult for you to make a unique contribution. Additionally, if someone is actively curating the page, possibly preparing it for submission as a good or featured article, he or she may not welcome someone jumping in and making wholesale revisions. Please avoid such topics.
Also avoid very broad topics, since these are difficult to research and cover comprehensively. Examples of topics that are too broad are “lifestyle,” “healthcare,” or “public policy,” for example.
A topic that is more appropriate is “Public Policy in Argentina” or “Healthcare in Portugal.”
Parent Wikipedia articles will typically have a set of links to related incomplete articles at the bottom of the page. For example, the “Domestic Violence” Wiki page has a section called “By Country” that lists links to other pages such as “Domestic Violence in Ecuador,” which may be incomplete. The “Healthcare” parent article also has links to incomplete articles such as “Healthcare in Somalia.”