From the DW:
"US bolsters security requirements for visa-free travel"
The new measures have formed part of a security-focused White House policy to curb irregular migration and increase security. A senior US official said "an adaptive and agile enemy" was the primary reason for the move. The US Department of Homeland Security (DHS) on Friday announced new security requirements for 38 countries whose citizens can currently travel to the country without visas. The countries, which include Germany and most European Union (EU) member states, must now use US counterterrorism information to screen travelers and launch public information campaigns if 2 percent of their citizens overstay their visas.
Announcing the new measures, Homeland Security Secretary Kirstjen Nielsen said:
^ It's important to keep the Visa Waiver Program and to keep those coming into the US by the VWP safe as well as American citizens. Hopefully these new security requirements will be followed by current VWP countries so that their citizens can continue to come to the US. ^