For a few years, peaking in the late 1990s and early 2000s, the U.S. courts seemed to accept that the First Congress had (maybe accidentally!?) created a statute that allowed foreigners to sue U.S. companies for complicity in human rights violations that took place overseas. It's actually just a single sentence: "The district courts shall have original jurisdiction of any civil action by an alien for a tort only, committed in violation of the law of nations or a treaty of the United States."
In some modern alien tort cases, the companies were accused of helping foreign governments commit such violations, as in this case; in other cases, the companies were accused of asking the foreign governments to do so (to protect their interests).
What we see here is basically the Supreme Court completing a process of saying that that's not actually what that old law is about and that it can't be used this way, pretty much at all.
I understand the issue that the First Congress probably didn't intend such a broad notion of "the law of nations" and also possibly didn't intend to create indirect liability for those who play a role in these abuses without actually carrying them out. (The decision notes that there's a much more recent statute that allows suing actual perpetrators: it's clearly just harder to get them into court in the U.S. most of the time.) It's kind of sad because the practical reality is often that courts in many countries aren't very independent, so a lot of victims of various abuses find it hard to get a domestic legal remedy for what's been done to them.
In this case I recall there was some strong evidence that some Cisco employees knew that they were being asked to help the Chinese government identify Falun Gong members (and that the government would probably do bad stuff to those people), and that they even gave monitoring Falun Gong as a use case or example in some of their product marketing. What we're told by this decision is that there isn't a clear U.S. legislative basis for a legal remedy against Cisco for this, if almost all of the relevant actions happened in China.
Maybe this is an opportunity for an attempt to amend U.S. law to state that U.S. companies have some responsibility to stop their foreign subsidiaries from doing stuff like this (although the actual legislative definition of "stuff like this" would presumably be a thorny question).