Writing and illustrations in periodicals are important historical artifacts. Poole's Index to Periodical Literature 1802-1881 Ref. Newspapers are published everywhere in many languages. Back issues are almost always available only as microfilm. Most newspapers available in microfilm can be obtained through Interlibrary Loan.
Few newspapers have indexes to their contents, but some of the most important ones do.
New York Times Index 1851-date. An excellent directory to resources worldwide.