Section 2333(d)(2) in part imposes civil liability on “any person who aids and abets, by knowingly providing substantial assistance, or who conspires with the person who committed such an act of international terrorism.” Ps have brought suit against three of the largest social-media companies in the world-Facebook, Twitter (D), and Google (which owns YouTube)-for allegedly aiding and abetting ISIS. ISIS has used Ds’ social-media platforms to recruit new terrorists and to raise funds for terrorism. P claimed that Ds allegedly knew that ISIS was using their platforms but failed to stop it from doing so. This case arises from a 2017 terrorist attack on the Reina nightclub in Istanbul, Turkey. The attack was carried out by Abdulkadir Masharipov. After planning and coordinating the attack with ISIS emir Abu Shuhada, Masharipov entered the Reina nightclub in the early hours of January 1, 2017, and fired over 120 rounds into a crowd of more than 700 people. Masharipov killed 39 people and injured 69 others. The next day, ISIS released a statement claiming responsibility for the attack. Two weeks later, Masharipov was arrested in Istanbul after hiding out in ISIS safe houses. Nawras Alassaf, who was killed in the attack. His family then brought the present lawsuit under §2333, alleging that they had been injured by the attack. ISIS and its adherents have used Ds for years as tools for recruiting, fundraising, and spreading their propaganda. ISIS’ videos and messages were then matched with other users based on those users’ information and use history. And, like most other content, advertisements were displayed with ISIS’ messages, posts, and videos based on information about the viewer and the content being viewed. ISIS’ videos and messages celebrated terrorism and recruited new terrorists. For example, ISIS uploaded videos that fundraised for weapons of terror and that showed brutal executions of soldiers and civilians alike. Ps allege that these platforms have been crucial to ISIS’ growth, allowing it to reach new audiences, gain new members, and spread its message of terror. Ps allege that Ds have known that ISIS has used their platforms for years. YPs claim that D have failed to detect and remove a substantial number of ISIS-related accounts, posts, and videos. Ps aver that Ds “have failed to implement . . . a basic account detection methodology” to prevent ISIS supporters from generating multiple accounts on their platforms. Ps assert that ds aided and abetted ISIS by knowingly allowing ISIS and its supporters to use their platforms and benefit from their “recommendation” algorithms, enabling ISIS to connect with the broader public, fundraise, and radicalize new recruits. And, in the process, Ds allegedly have profited from the advertisements placed on ISIS’ tweets, posts, and videos. Ps allege that Google (D) has reviewed and approved some ISIS videos thereby sharing some amount of ad revenue with ISIS. The Court dismissed the complaint for failure to state a claim. The Ninth Circuit reversed, finding that plaintiffs had plausibly alleged that Ds aided and abetted ISIS within the meaning of §2333(d)(2) and thus could be held secondarily liable for the Reina nightclub attack. D appealed.