Across Europe, leaders for years have promised to ramp up defense spending, though progress has been slow. NATO in 2014 set a target that each member dish out 2 percent of its GDP on defense by 2024.

President Trump said Thursday that NATO had to remain “strong” — as the military alliance’s top official praised him for sparking a “staggering” boost in military ...

NATO members will have to bolster their defense spending by “considerably more than 3%” of their GDP, the alliance’s Secretary General Mark Rutte said Saturday. The alliance chief’s ...