Mattis's NATO Threat Won't Scare America's Allies

U.S. Defense Secretary James Mattis has delivered to America's allies a message often heard during Donald Trump's election campaign: Spend more on defense or expect the U.S. to "moderate its commitment to the alliance." While European members of the North Atlantic Treaty Organization have agreed, they won't necessarily rush to meet U.S. demands.

In 2014, NATO members reaffirmed their commitment to spend 2 percent of their economic output on defense and 20 percent of that amount "on major new equipment, including related research and development." The U.S. wants them to stick to these top-line promises. But 2 percent and 20 percent are only numbers. As John Deni of the U.S. Army War College wrote in a 2015 blog post for the Carnegie Endowment, Greece consistently spends 2 percent of its gross domestic product on defense -- a model U.S. ally on that count -- but when it comes to actual fighting, Denmark, which has averaged 1.5 percent of GDP in defense spending since 2000, provides more troops and more aircraft, takes part in riskier missions, and suffers more casualties.