Travel Alerts relate to short term conditions which may pose risks to U.S. citizens. This is the U.S. State Department's list of active travel alerts.
The Department of State's list of active travel warnings, includes details as to why the country is judged to be dangerous and how to obtain help from the U.S. consulate or other source.
The official website of the State Department's Bureau of Consular Affairs, travel.state.gov/ offers information on a variety of issues related to foreign travel. Travel warnings ("long-term, protracted conditions") and travel alerts ("short-term conditions...that pose imminent risks").