4 TWITTER, INC. v. TAAMNEH Syllabus actionable wrong—here, an act of international terrorism. However, that does not require a strict nexus between the assistance and the wrongful act; defendants are liable for other torts that are the foreseeable risk of an intended tort, and an aider and abettor can assist someone without knowing all the details of his plan. Plus, in appropriate circumstances, a defendant’s role in an illicit enterprise can be so systemic and intentional that the defendant aids and abets each act of the enterprise—as in Halberstam itself. To summarize the requirements of §2333(d)(2), the phrase “aids and abets, by knowingly providing substantial assistance” points to the elements and factors articulated by Halberstam. Those elements and factors should not be taken as inflexible codes but should be understood in light of the common law and applied as a framework designed to hold defendants liable when they consciously and culpably “participate[d] in” a tortious act in such a way as to help “make it succeed.” Nye & Nissen v. United States, 336 U. S. 613, 619. Pp. 17–21. (c) Plaintiffs have satisfied Halberstam’s first two elements by alleging both that ISIS committed a wrong and that defendants knew they were playing some sort of role in ISIS’ enterprise. But plaintiffs’ allegations do not show that defendants gave such knowing and substantial assistance to ISIS that they culpably participated in the Reina attack. Pp. 21–30. (1) Plaintiffs allege that defendants aided and abetted ISIS in the following ways: First, they provided social-media platforms, which are generally available to the internet-using public; ISIS was able to upload content to those platforms and connect with third parties on them. Second, defendants’ recommendation algorithms matched ISIS-related content to users most likely to be interested in that content. And, third, defendants knew that ISIS was uploading this content but took insufficient steps to ensure that its content was removed. Plaintiffs do not allege that ISIS or Masharipov used defendants’ platforms to plan or coordinate the Reina attack. Nor do plaintiffs allege that defendants gave ISIS any special treatment or words of encouragement. Nor is there reason to think that defendants carefully screened any content before allowing users to upload it onto their platforms. None of plaintiffs’ allegations suggest that defendants culpably “associate[d themselves] with” the Reina attack, “participate[d] in it as something that [they] wishe[d] to bring about,” or sought “by [their] action to make it succeed.” Nye & Nissen, 336 U. S., at 619 (internal quotation marks omitted). Defendants’ mere creation of their media platforms is no more culpable than the creation of email, cell phones, or the internet generally. And defendants’ recommendation algorithms are merely part of the infrastructure through which all the content on their platforms is filtered. Moreover, the algorithms have been