European migrant crisis

The United States government implements new restrictions to its visa waiver program which now requires, with limited exceptions, European, Japanese and Australian travelers to the United States who either have been visitors in the last five years to or are dual-citizens of Iran, Iraq, Syria and Sudan to obtain a travel visa. The new visa policies were mandated by legislation which was passed, in the aftermath of November 2015 Paris attacks, by Congress on the grounds of national security.

Sources:  CNN  Radio Free Europe/Radio Liberty  The New York Times