Bangladesh, May 7 -- The administration of Donald Trump has unveiled a sweeping new national counterterrorism strategy that sharply criticizes European allies, accusing parts of the continent of becoming breeding grounds for extremism due to mass migration, weak border controls, and political reluctance to confront Islamist radicalism. The document, released by the White House, marks one of the strongest public rebukes of Europe by a modern US administration and signals a renewed “America First” approach to global security.

The 16-page strategy outlines what Washington sees as the principal terrorist threats facing the United States and its allies. It identifies three primary categories of danger: transnational drug cartels a...