The Department of State's Office of the Historian offers digital volumes of the Foreign Relations of the United States series. These contain documents regarding US relations with specific nations. Volumes are generally organized by year, and you will have to look for documents relating to Mexico.
The New York Times Archive searches the contents of the New York Times from 1851 to present. Full text is provided to Murray State users. Murray State users must create an account to authenticate access, AND MUST BE ON CAMPUS FOR REGISTRATION. Following registration, access is available off-campus. Visit https://www.nytimes.com/activate-access/ippass to create a free account. If you are unable able to come to campus to create your account, please contact Cris Ferguson .
Provides easily-searchable first-hand accounts and coverage of the Wall Street Journal from 1889 to 2011.