What does "US jurisdiction" mean for travellers and why is it important?
Because, if you are under US jurisdiction, then travel to Cuba through the US is always governed by US Laws.
Check here if you are unsure, because while this applies to all US citizens, it also applies all travel initiated from the USA irrespective of your nationality :
The USA has the "Trading With the Enemy" Act and names Cuba, along with other countries, for particular attention under its legislative powers which are carried out under Regulations.
The Office of Foreign Asset Control (OFAC) is tasked with administering and enforcing the Regulations via economic and trade sanctions against Cuba, and this includes travel related activities, but not immigration.
OFAC prohibits travel to Cuba for "tourism".
However, Cuba allows tourists from the US, and to enter the country a traveller must have a valid Cuban Visa. Your chosen carrier will usually advise you how to obtain your visa, which in most cases will actually be called a Tourist Card.
OFAC's Regulations and Cuban immigration laws must never be confused - they exist in different universes!
So that's the context.
Despite the Regulations, going to Cuba for most people is actually now much easier to navigate, because the rules have been clarified.
OFAC allows any traveller to "self certify" that they meet a category of authorised travel to Cuba. See the thread in this forum about travelling to Cuba from 9 November as it links to the details underpinning each category of travel.
Whoever carries you to Cuba will ask what category you chose, and must retain that record for at least 5 years, because that is what OFAC requires of carriers.
Is it that easy?
You made a lawful undertaking to satisfy an OFAC category of authorised travel. So there's one more step you should take if you want that peace of mind that you are "compliant", and it's to be prepared to develop an itinerary. That's relatively easy if, for example, you self certify under the "support for the Cuban people" category. We intend to post further guidance in this forum, but in the meantime consult OFAC, particularly their linked Q&As. The key to your itinerary is that it reads to show a schedule of activities which does not include free time or recreation in excess of that consistent with a full-time schedule.
So, I am now in Cuba. I know I have to comply with Cuban law, but am I still under US Jurisdiction?
You made lawful undertakings, and while they allowed you to travel, OFAC also introduced a new Regulation about direct financial transactions with entities and subentities on the Cuba Restricted List. They are also identified elsewhere in this forum, and below we will explain why this is unlikely to affect the majority of travellers to Cuba, unless they choose to make an accommodation booking direct with a named entity/subentity.