I'm from The Netherlands and travelled to the US (Los Angeles) last summer under the Visa Waiver Program (VWP/ESTA).
I plan to visit Los Angeles again this summer.
The ESTA I have is valid for 2 years and will still be valid on arrival. However if I were to apply for an ESTA today it will be denied. That is because I have visited North Korea last month.
The Visa Waiver Program states that:
Travelers in the following categories are no longer eligible to travel or be admitted to the United States under the Visa Waiver Program (VWP):
Nationals of VWP countries who have traveled to or been present in Iran, Iraq, North Korea, Sudan, Syria, Libya, Somalia and Yemen on or after March 1, 2011 (with limited exceptions for travel for diplomatic or military purposes in the service of a VWP country). Nationals of VWP countries who are also nationals of Iran, Iraq, North Korea, Sudan, or Syria.
If I travel to LA today, do I need to apply for a visa or can I travel on the approved ESTA? In fact. North Korea does not stamp the passport so it's not obvious that I visited the country. The only way they can see is by looking at the entry stamp from China. The chinese city bordering North Korea, Dandong, is written in Chinese on the entry stamp.