Leaving the country

Hello Rabbi,
 
I saw that you wrote in response to the question that you are too old to leave the country, and that you completely understand people who decide to leave the country due to the social situation. (I may be wrong in the wording. I was unable to find the question on the website)
I know that there is a prohibition against leaving the country, except in specific cases. Where does the halakhic permission to leave the country come from due to the current social situation?