President Donald Trump on Wednesday touted a plan for NATO member states to raise defense spending to 5 percent of their gross domestic product (GDP) as a “monumental win” for the United States.The agreement addresses Trump’s long-standing concern about NATO members not carrying their weight. Newsweek reached out to the alliance for comment via email.Why It MattersNATO leaders committed increasing their defense spending on Wednesday following pressure from Trump, who for years has raised concerns that the U.S. was paying more than its fair share of spending. Under the plan, nearly every country in the military alliance will increase investments to the 5 percent by 2035.Leaders wrote in a declaration that the agreement is reaffirmation to their “ironclad commitment to collective [defense] as enshrined in Article 5 of the Washington Treaty,” which states that an attack on one NATO member shall be treated as an attack against all.The agreement was signed with a backdrop of a world dealing with crises. The yearslong war between Russia and Ukraine continues. World leaders have been trying, but struggling, for years to broker a deal to end the armed conflict. Meanwhile, tensions have flared up in the Middle East amid the battle between Iran and Israel, with Trump striking several Iranian nuclear facilities over the weekend. Iran has since retaliated against U.S. military bases, and Trump has pushed for a ceasefire.What To KnowThe agreement means many NATO countries will be dramatically increasing their defense investments over the coming years, as many are far from the 5 percent mark. The declaration states that the spending must be on “core defense requirements” as well as “defense-and security-related spending.””Our investments will ensure we have the forces, capabilities, resources, infrastructure, warfighting readiness, and resilience needed to deter and defend in line with our three core tasks of deterrence and defense, crisis prevention and management, and cooperative security,” the declaration reads.At the moment, Poland is the NATO member state spending the most per GDP on defense investments, according to the latest data from the alliance, at 4.12 percent. Estonia follows with 3.43 percent and the U.S. places third with 3.38 percent. Conversely, Belgium, Canada, Italy and Spain each spend less than 1.5 percent.Trump celebrated the declaration in remarks to reporters on Wednesday.”In a very historic milestone this week, the NATO allies committed to dramatically increase their defense spending to that 5 percent of GDP, something that no one really thought was possible, and they said, ‘You did it sir, you did it.’ I don’t know if I did it, but I think I did,” Trump said.The president said it will add more than $1 trillion per year to common defense. “This is a monument, really, to victory. But it’s a monumental win for the United States because we were carrying much more than our fair share.”Spain Says It’s Unable to Meet Spending Requirement, Sparks Trump’s IreSome NATO member states have expressed concerns about whether it is realistic to increase defense spending so much over the next decade. Spain has already said it will not be able to do so, with Prime Minister Pedro S谩nchez describing the requirement as “unreasonable,” the Associated Press (AP) reported.He announced a deal earlier this week that would allow Spain to remain part of NATO without having to increase defense spending to 5 percent of its GDP.”We must protect Europe. But we must also protect what makes it unique in the world: its welfare state and its commitment to diplomacy, development aid, and peace,” he wrote in a post to X, formerly Twitter.However, Trump expressed frustration. “I think Spain is terrible, what they’ve done. They’re the only country that won’t pay the full鈥攖hey want to stay at 2 percent. I think it’s terrible. And you know, they’re doing very well. Their economy is doing very well. And that economy could be blown right out of the water with something bad happening,” he said.He added that he could make Spain “pay twice as much” as he negotiates a trade deal with Madrid.What People Are SayingNATO leaders wrote in their declaration: “We reaffirm our shared commitment to rapidly expand transatlantic defense industrial cooperation and to harness emerging technology and the spirit of innovation to advance our collective security. We will work to eliminate defense trade barriers among Allies and will leverage our partnerships to promote defense industrial cooperation.”United Kingdom Prime Minister Keir Starmer said, per the AP: “This is the moment to unite, for Europe to make a fundamental shift in its posture and for NATO to meet this challenge head-on.”What Happens NextNATO members have until 2035 to increase their spending to comply with the declaration. How Trump’s negotiations play out with Spain has yet to be seen.