President Trump defended his decision Thursday night to launch cruise missiles into Syria, saying the strike mattered to U.S. national security.

“It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons,” Trump said at his Mar-a-Lago resort in Florida roughly an hour after the missiles hit their targets.

Trump claimed “there can be no dispute that Syria used banned chemical weapons” and that “numerous previous attempts at changing [Syrian President Bashar] Assad’s behavior have all found and failed very dramatically.”

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U.S. warships launched more than 50 cruise missiles at a Syrian airbase in response to a chemical attack believed to be carried out by forces loyal to Assad.

The United States' attack was the culmination of a rapid shift of Trump’s views on the Syrian civil war, which began in 2011.

He opposed U.S. involvement and repeatedly railed against U.S. military interventions in the Middle East just less than a year ago, during his presidential campaign.

Critics questioned how the attack fit into Trump's "America first" slogan.

Trump also used deadly force abroad without seeking congressional approval, which lawmakers from both parties quickly noted on Thursday evening.

A number of U.S. lawmakers urged caution , warning that such attacks usually require approval from Congress.

Trump called on “all civilized nations” to join the U.S. in bringing the war in Syria to an end.

“We hope as long as America stands for justice and peace and harmony will in the end prevail,” he said.