The Hague. NATO leaders gathered in the Netherlands on Tuesday for a historic two-day summit that could unite the world’s biggest security organization around a new defense spending pledge or widen divisions among the 32 allies.

The allies are likely to endorse a goal of spending 5 percent of their gross domestic product on their security, to be able to fulfill the alliance’s plans for defending against outside attack. Still, Spain has said it cannot, and that the target is "unreasonable." President Donald Trump has said the United States should not have to.

Slovakia said that it reserves the right to decide how to reach the target by NATO's new 2035 deadline.

“There’s a problem with Spain. Spain is not agreeing, which is very unfair to the rest of them, frankly,” Trump told reporters on Air Force One on his way to the summit.

NATO's first summit with Trump, in 2018, unraveled due to a dispute over defense spending.

Ahead of the meeting, Britain, France, and Germany committed to the 5 percent goal. The host country, the Netherlands, is also onboard. Nations closer to the borders of Ukraine, Russia, and its ally Belarus had previously pledged to do so.

“We are not living in happy land after the Berlin Wall came down. We are living in much more dangerous times and there are enemies, adversaries who might want to attack us,” NATO Secretary-General Mark Rutte said ahead of the summit in The Hague.

“We have to make sure that we defend our beautiful way of life and systems and our values,” he said.

Trump’s first appearance at NATO since returning to the White House was supposed to center on how the US secured the historic military spending pledge from others in the security alliance -- effectively bending it to its will.

But the spotlight has shifted to Trump’s decision to strike three nuclear enrichment facilities in Iran that the administration says eroded Tehran’s nuclear ambitions, as well as the president’s sudden announcement that Israel and Iran had reached a “complete and total ceasefire.”

Ukraine has also suffered as a result of that conflict. It has created a need for weapons and ammunition that Kyiv desperately wants, and shifted the world's attention away. Past NATO summits have focused almost entirely on the war in Ukraine, now in its fourth year.

Still, Rutte insisted NATO could manage more than one conflict at a time.

“If we would not be able to deal with ... the Middle East, which is very big and commanding all the headlines, and Ukraine at the same time, we should not be in the business of politics and military at all," he said. "If you can only deal with one issue at a time, that will be that. Then let other people take over.”

Ukrainian President Volodymyr Zelensky arrived in The Hague for a series of meetings, despite his absence from a leaders’ meeting aiming to seal the agreement to boost military spending.

It’s a big change since the summit in Washington last year, when the military alliance’s weighty communique included a vow to supply long-term security assistance to Ukraine, and a commitment to back the country “on its irreversible path” to NATO membership.

Zelensky’s first official engagement was with Dutch caretaker Prime Minister Dick Schoof at his official residence just across the road from the summit venue.

But in a telling sign of Ukraine’s status at the summit, neither leader mentioned NATO. Ukraine’s bid to join the alliance has been put in deep freeze by Trump.

“Let me be very clear, Ukraine is part of the family that we call the Euro-Atlantic family,” Schoof told Zelensky, who in turn said he sees his country’s future in peace “and of course, a part of a big family of EU family.”

Schoof used the meeting to announce a new package of Dutch support to Kyiv, including 100 radar systems to detect drones and a move to produce drones for Ukraine in the Netherlands, using Kyiv’s specifications.

The US has made no new public pledges of support to Ukraine since Trump took office six months ago.

Meeting later with Rutte and top EU officials, Zelensky appealed for European investment in Ukraine's defense industry, which can produce weapons and ammunition more quickly and cheaply than elsewhere in Europe.

“No doubt, we must stop (Russian President Vladimir) Putin now and in Ukraine. But we have to understand that his objectives reach beyond Ukraine. European countries need to increase defense spending," he said, adding that NATO's new target of 5 percent of GDP "is the right level.”

He thanked them for their unity in supporting Ukraine, saying: “I think this is the most important thing.”