On top of that, the allies will dedicate 1.5% of their GDP to upgrading infrastructure — roads, bridges, ports and airfields — needed to deploy armies to the front. Money spent on protecting networks or preparing societies for future conflict can be included.

The two-day summit has been overshadowed by Trump's decision to order the bombing of nuclear installations in Iran. In 2003, the U.S.-led war on Iraq deeply divided NATO, as France and Germany led opposition to the attack, while Britain and Spain joined the coalition.

The leaders reaffirmed their “ironclad commitment” to NATO’s collective defense clause, Article 5. In recent years, Trump had sowed seeds of doubt about whether the U.S. — NATO’s most powerful member — would come to the aid of any ally under attack.