DP kinda started because the State Department didn't quite know if the country they worked in was dangerous or not. Or they were political harangues. Now they do a much better job but for some reason they refuse to include U.S. destinations. Ideally they would've the best access to crime against tourists and visitors.
http://www.businessinsider.com/state-de ... tem-2018-1Level 1 - Exercise Normal Precautions: This is the lowest advisory level for safety and security risk. There is some risk in any international travel. Conditions in other countries may differ from those in the United States and may change at any time.
Level 2 - Exercise Increased Caution: Be aware of heightened risks to safety and security. The Department of State provides additional advice for travelers in these areas in the Travel Advisory. Conditions in any country may change at any time.
Level 3 - Reconsider Travel: Avoid travel due to serious risks to safety and security. The Department of State provides additional advice for travelers in these areas in the Travel Advisory. Conditions in any country may change at any time.
Level 4 - Do Not Travel: This is the highest advisory level due to greater likelihood of life-threatening risks. During an emergency, the U.S. government may have very limited ability to provide assistance. The Department of State advises that U.S. citizens not travel to the country or leave as soon as it is safe to do so. The Department of State provides additional advice for travelers in these areas in the Travel Advisory. Conditions in any country may change at any time.
To check each country's level, you can visit a newly updated State Department Travel Advisory website. There's also a color-coordinated map that you can browse.
Some examples of countries listed at level two at the time of publication include Mexico, due to crime in certain areas, and the United Kingdom, due to elevated risks of terrorism. Level three countries include Russia, due to civil unrest in certain areas, and Venezuela, due to crime and a limited ability of the US to provide assistance to citizens. Level four countries include Iraq, Iran, and Libya.