LONDON — Around the world, growth has been slowing, trade and investment have been falling, and now, war in the Middle East could jolt markets.

But governments across Europe and in Britain face an additional economic stress — significantly raising military spending. These peacetime economies have to figure out how to deter Russia, a belligerent foe that is already on a wartime footing and spending an estimated 7.5% of its national income on its military.

The debate has intensified in the run-up to NATO’s annual summit meeting this week at The Hague, where the security alliance will set new spending goals. President Donald Trump has demanded that the other 31 NATO members devote 5% of their total economic output to defense, up from the current 2% target. He has also made clear that the United States will reduce its financial and troop commitments, though it is unclear by how much.

This is a “global reset,” Lt. Gen. Sean Clancy, the new chief of the European Union’s military committee, said at a security conference in Brussels this month. But “we haven’t even defined what the transition looks like.”

Money, though, is far from the only issue Europe confronts now that it has reluctantly accepted the reality that it must be able to protect itself without help from the United States.

Formidable political, strategic and regulatory hurdles remain. EU leaders must maintain public support for common military spending and joint weapons procurement, even as right-wing nationalist sentiments oppose giving the bloc more power.

And the farther from the Russian border, the less urgent the threat feels. Poland, for instance, is already spending nearly 5% of its gross domestic product on defense while Spain dedicated just 1.3% last year.

The European Union and Britain must also figure out how to prepare for the new kind of war that Russian aggression presents.

Since the fall of the Soviet Union, Europe’s military has been focused on deploying troops to hot spots like Afghanistan and Iraq. Now they must be able to defend their own territory. Intelligence officials warn that Russian forces could be ready to attack a NATO country in five years.

Complicating the decision-making are rapid advancements in intelligence, surveillance, battlefield management and cyber technologies.

Look at Ukraine’s battlefields. They are dominated by new technologies and throwback strategies, millions of drones and muddy trenches.