BRUSSELS — Weeks after being berated by President Trump for failing to spend enough on defense, European nations vowed Thursday to boost military cooperation in their part of the world. At a summit in Brussels, the 28 European Union leaders — 22 of them from nations that also are members of the U.S.-led NATO alliance — agreed to jointly develop or purchase military equipment such as drones. “The objective is to deliver capabilities, ensure a competitive, innovative and balanced basis for Europe’s defense industry across the EU,” they said in a statement. EU countries plan to draw up criteria and binding commitments over the next three months for setting their defense cooperation goals in stone instead of relying on the vaguer promises of the past. The leaders also agreed to use EU funds to finance Europe’s battle groups — small, expeditionary forces that can be deployed quickly to crisis hotspots. While the moves are modest in comparison to NATO, they mark a sea change in the way the EU thinks about defense, faced with an increasingly belligerent Russia and an unpredictable partner in Washington.