On Thursday, April 6, President Donald Trump ordered his first military action since becoming commander in chief. In the attack, 59 Tomahawk cruise missiles were launched from U.S. Navy ships in the Mediterranean Sea and aimed at a Syrian airfield in al-Shayrat, reportedly damaging Syrian military supplies and killing six Syrian soldiers at the air base and nine civilians from surrounding villages, according to Syrian officials.

This attack is the first from the U.S. on Syrian government forces.

Why did Trump order the attack?

The president has stated in the past that he was against attacks on the regime of Syrian President Bashar al-Assad. However, that changed on Tuesday, April 4, when the regime made a chemical weapons attack on civilians in Northwestern Syria.

At least 86 people, including 26 children, were killed when warplanes dropped bombs on the town of Khan Sheikhoun, as reported by CNN.  The international aid group Doctors Without Borders said those near the blast were exposed to chemical weapons.

The Syrian government previously claimed it had destroyed its entire stockpile of toxic weapons in 2014 through a Russian-U.S. deal. The deal was initiated after al-Assad was accused of using chemical weapons in a 2013 attack against his own people near Syria’s capital city, Damascus. Al-Assad denied the accusation.

The Syrian government denied involvement in the attack on Khan Sheikhoun, as well. However, many countries, including the U.S., say they have intelligence leading them to believe al-Assad ordered the attack.

U.S. Secretary of State Rex Tillerson said, “There is no doubt in our minds that Syria and the regime under Bashar Assad were responsible for this attack.”

U.S. Ambassador to the United Nations Nikki Haley said, “The joint investigative mechanism has found beyond any doubt that the Syrian regime has used chemical weapons against its own people multiple times.”

The air base on which Trump ordered the missiles is believed to host the warplanes that carried out the chemical weapons attack on civilians.

The Pentagon said the intention of the strike was to “deter the regime from using chemical weapons again.”

“The United States took a very measured step last night,” Haley told the UN. “We are prepared to do more. But we hope that will not be necessary. It is time for all civilized nations to stop the horrors that are taking place in Syria and demand a political solution.”

Why is this significant?

The U.S. began launching airstrikes in Syria in 2014, but the terrorist group ISIS was the target of those attacks. After 2013, when al-Assad’s forces are believed to have ordered a chemical weapons attack on civilians, then-President Barack Obama received harsh criticism for threatening retaliation but never acting.

Thursday’s attack creates a tricky situation with Russia, Syria’s biggest ally. Russian President Vladimir Putin released a statement saying the U.S. missile strike “dealt a serious blow to Russian-U.S. relations, which are already in a deplorable shape.”

According to Pentagon spokesman Capt. Jeff Davis, the U.S. military notified Russia of the strike beforehand, to avoid killing any Russians onsite at al-Shayrat. In response to the attack, Russia has announced it will stop exchanging information with the U.S. about its flights over Syria, a deal originally intended to avoid incidents in the crowded Syrian skies. Russia also called for a meeting of the UN Security Council.

Was this legal?

The question of the legality of this attack is tricky, as most things regarding presidential war powers are. Trump carried out this attack without the approval of Congress or the UN Security Council.

In regard to international law, the UN did not approve the attack, and the intention of the attack was not self-defense. Therefore, the attack breaks the UN Charter, which says a country must cite one of those two conditions to authorize an attack on a member nation’s soil.

To reporters, Tillerson has cited Syria’s violation of the international laws on chemical weapons as justification for the attack. Additionally, in the past, human rights advocates have argued that international law justifies an attack “to stop an atrocity,” which Trump has argued Syria’s chemical weapons attack was.

In terms of domestic legality, the U.S. Constitution says the president must receive Congressional approval before carrying out an attack on another nation, unless the U.S. is under attack. This, however, is not exactly how the past presidents have treated their powers as commander in chief.  Trump cited a national security interest as his rational for the legality of the attack.

Russia and Iran, both allies of Syria, have called the attack a violation on international law. However, the Trump administration has earned praise from many countries who have come out in support of the missile strike, including the United Kingdom, Germany, Australia, Saudi Arabia and Turkey.