Calling for a debate on the United States’ use of drones to a crowd of about 40 students Thursday afternoon, Law School professor Oona Hathaway LAW ’97 homed in on several legal issues surrounding drones that she described as important for Americans in the coming years.

During the talk, entitled “The Legality of Drone Strikes,” Hathaway said drones — unmanned aerial vehicles whose purposes range from surveillance to targeted killings — have become more central to the United States’ missions abroad in recent years. She said drone use has presented three key challenges to the United States: the erosion of checks on the president’s power to wage war, the proliferation of drones at home and abroad and the threat to civil liberties posed by their use. Hathaway, who serves on the Advisory Committee on International Law for the legal adviser at the State Department, warned that the precedents currently being set regarding drone usage could be dangerous and lead to a society in which Americans’ rights are not protected.

“Drones are increasingly what the U.S. is relying upon in order to protect us,” Hathaway said. “Trained boots on the ground are becoming less and less a part of the U.S. military.”

Drones have killed over 1,900 Pakistanis in tribal areas since 2006, Hathaway said, adding that the Unites States has used drones in Afghanistan, Pakistan, Yemen, Somalia, Iraq and Libya.

Hathaway, who directs the Center for Global Legal Challenges at Yale Law School, said drone strikes are difficult to defend legally, though she added that some uses of drones by the American military could be justified under international law. She said the drone strikes in Pakistan could be one such example because Pakistan has probably consented to the strikes, although the country has denied such allegations.

Hathaway also warned that the United States’ drone strike policy compromises the government’s separation of powers.

“[Drone strikes] make it easier for the president to exercise war-making power without any checks,” she said. “[Drone strikes] threaten to very much upset traditional powers over use of military force.”

Under the War Powers Resolution of 1973, the president may use force without Congress’s permission for 60 days, after which he or she needs congressional approval. President Barack Obama, Hathaway said, used force in Libya for more than 60 days without deferring to Congress and argued that such actions were legal in part because the United States military used drones rather than troops, and American lives were not at stake as a result. Hathaway said this argument created a dangerous precedent, and she emphasized that no other branch of the American government signed off on the military action in Libya.

Hathaway also noted the rising use of drones by other countries, particularly China, Turkey and Israel, and warned that terrorist groups such as Hamas and Hezbollah have expressed interest in obtaining drones. She said the United States would have to consider establishing rules for drone use in a world where other countries could use unmanned aerial vehicles to attack the U.S.

“If we’re making arguments now about drones, others are going to be making those back at us in a very short amount of time,” she said.

Four students interviewed at the talk said they think Hathaway adequately covered the legal issues surrounding drone strikes. Still, two students said they wished Hathaway addressed some of the more controversial aspects of drone use, including the moral implications.

Dure Aziz Amna ’15, a student from Pakistan, said she hoped Hathaway would address the ethical concerns surrounding drone use.

“As someone coming from Pakistan, the moral issues are just as important as the legal ones,” Amna said.

Carl Sandberg ’14, president of the International Students’ Organization, which co-sponsored the talk, said he thinks the United States must begin to think critically about drone use policy.

Hathaway has taught continuously at Yale Law School since 2009.

Correction: Feb. 23 

A previous version of this article mistakenly referred to the International Students’ Organization as the International Student Association.