As I understand it quite a lot of US Federal law is based on 'common law'. This is also true for many states, although I think some jurisdictions have 'civil law' roots instead.

Since common & civil law originally derived from the prior political situations of the US (e.g., many were British, French, Spanish, etc. colonies or territories): since the US became an independent country have there ever been changes to US law via common or civil law which originated with changes to another nation's laws? And/or is this possible today?

This question is based on the principle that much law is derived from precedent, not all of which is encoded in written documents.

An interesting corollary would be if US law could influence the laws in other countries based on the same principle.

By the way, my use of quotations is because I am not a lawyer but I believe these terms have specific technical meanings.

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    Louisiana is the only civil law state in the US, but its legal system has taken on an unusual number of common-law features because of its relationship to the US federal system. Similar effects have been felt in Puerto Rico (a US territory), the Philippines (a former US territory), and Quebec (a Canadian province).
    – phoog
    Commented Apr 13, 2019 at 2:16

1 Answer 1


I'm not sure it fully qualifies as an appropriate answer, since it was de facto law before the US existed ... and I'm not entirely sure what the statutes were between when the US declared independence and when it had its first constitution ... but the Spanish dollar was legal tender in the US, coexisting with the US dollar, until 1857. That makes it an externality that turned into US law, arguably owing to pragmatism but also because the USD was of very similar weight.

A more recent example might simply be Roe vs Wade. No law was passed, but because abortion was becoming legal elsewhere, because of on the ground activists, and because of activist lawyers who filed lawsuits, SCOTUS ended up sensing the winds of change, took on a case (or the latter two the other way around, but it doesn't matter), and basically legalized abortion without getting Congress involved. It's probably stretching the truth to say that SCOTUS changed the law only because of foreign influence, but I can't imagine a scenario where the latter didn't play a role as Justices wondered what was happening elsewhere. Similarly for gay marriage, or for the ongoing cases that are trying to make their way to the Supreme Court to legalize marijuana or ban child corporal punishment.

The situation the other way around, with US law become another country's law, happens basically every day: because of 1st amendment free speech protection, just about anyone anywhere can publish to their heart's content with a large degree of impunity. It might not be accessible to the locals in their country, and whoever does publish might end up prosecuted in their country if their government finds out who they are ... but they can publish it if they've the technical skills to work around whatever firewall they're behind, and their fellow citizens can read what they publish if they have that skillset too. It's not technically a law change, of course, but it's prompting other countries to look into whether the law or how it's enforced should be changed. (I'd also point out in passing that it works the other way around for speech restrictions. Hardly any news outlet ill will publish prophet depictions and caricatures.)

A more concrete and related example are the provisions in US law to protect online platforms like Facebook or Twitter. (Section 230 if memory serves me well, but I'd need to double check.) It basically led to the EU Copyright Act from a few weeks ago, which in one sense provides for the opposite by making platforms like Facebook liable for copyright infringements.

  • "arguably owing to pragmatism but also because the USD was of very similar weight": the weight of the US dollar was determined by weighing a bunch of (worn) Spanish dollars and using the resulting average. But money worked rather differently then from how it works now; the value was in the silver content. A quick internet search on Roe v Wade turns up no evidence that international developments had any influence on the court; can you add some support for that assertion?
    – phoog
    Commented Apr 13, 2019 at 2:21

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