Check out the UNH Franklin Pierce Law Library's Library Search for more books and ebooks on this topic. These survey texts will provide you with an overview of the basic premises of international law.
If you are researching to learn more about a country in general, its government, or its domestic laws it's good to get an overview. Try these sources:
CIA World Factbook - is a reference resource produced by the Central Intelligence Agency with almanac-style information about the countries of the world. It provides country profiles alphabetically by country. Note that while it may describe the style of government, population, economic indicators, etc. there are no sources cited. This is true for any legal details - there are no citations listed. Great for an overview and a place to start but not for in-depth legal research
JuriGlobe - A great resource for identifying a country's legal system. This is important when researching another country's domestic law (foreign legal research). If the country is a civil law country - you can expect to find that codes are significant sources of law, if a country is a common law country then case law will be very important. "Introductory Remarks" discusses how the authors categorized the different world legal systems - they describe that "[f]ive categories were selected for the creation of this Website on World Legal Systems: Civil law, Common law, Customary law, Muslim law, and Mixed law systems, the latter referring not to a single system but to a combination of systems."
The Foreign Law Guide (Brill - UNH Only)- provides you with more detail on a country's legal systems, political history, the structure of government and specific information (with citations) on common topics of law.
Websites
Law Library Resource Xchange –LLRX.com
This site includes a number of research guides on international law posted by law librarians as well as a search function.