I wouldn’t really call it a warning, they just stated the fact that the decision of being let in lays in the border officer’s hands. But if you count it, Poland has a travel warning for USA for years too: https://www.gov.pl/web/usa/idp , while being a long-standing strong supporter of the US.
It appears that these countries now have some form of warning associated with travelling to the USA:
Congrats US, not far to go to be on par with Afghanistan and Syria
I wouldn’t really call it a warning, they just stated the fact that the decision of being let in lays in the border officer’s hands. But if you count it, Poland has a travel warning for USA for years too: https://www.gov.pl/web/usa/idp , while being a long-standing strong supporter of the US.
By the way, the same “warning” applies to Canada: “in Canada, a border services officer makes the final decision on whether you are admissible or not”
Here’s how an actual travel warning looks like: https://www.gov.uk/foreign-travel-advice/myanmar
The Netherlands doesn’t have any particular warning regarding travelling to the US.