Original gTLDs are subject to US law. There could hypothetically be legislation that directs the Department of Commerce (who technically owns the original gTLDs

Original gTLDs are subject to US law. There could hypothetically be legislation that directs the Department of Commerce (who technically owns the original gTLDs) to not allow registrations to non-US entities, which Verisign would be obligated to enforce. New gTLDs are either corporate owned (.google) or were targeted at dotless domains (.diamonds). The ICANN SSAC killed the business model for the latter after companies had laid out millions, so they will likely face solvency issues in the coming years. ccTLDs are dependent on the political future of the government they are tied to (.ly and Libya is a good example), but at least you have a good idea up front of what you are hitching your cart to.