MUNICH — After years of encouraging European nations to work together to provide more of their own defense, the United States is having second thoughts, driven by concerns about NATO and possible protectionism in defense industries.

The new American skepticism has been the big surprise of the high-level security conference held this past week in Munich. And it has puzzled and disconcerted NATO officials, who have welcomed the European Union’s new commitment, after the Russian annexation of Crimea, to do more for its own defense.

Only last November, American and NATO officials embraced the bloc’s plans, under a program called the Permanent Structured Cooperation on Security and Defense, or Pesco, to spend more money on defense and to do it more efficiently, on national programs that would enhance European combat capacity and reduce overlapping national equipment that does not always work together with those of other allies.

The European Union created a defense research fund to provide 5.5 billion euros ($6.8 billion) a year in financing after 2020, a relatively modest sum, but one that could grow. As a psychological breakthrough, Pesco and the fund “mark a cultural revolution in Brussels,” the French defense minister, Florence Parly, said at the Munich conference.