Other democracies do generally have their own checks and balances. They might not be the same set of checks and balances as the US, but it's difficult to say as

Other democracies do generally have their own checks and balances. They might not be the same set of checks and balances as the US, but it's difficult to say as a whole that they are weaker. It's true that often the division of the executive and legislative branches is rather weak. But on the other hand there is often a stronger division between the judicial and other branches as judges are appointed independently. There are plenty of countries out there with very strong constitutional courts as well. I'm also not sure I agree that the US system is necessarily less sustainable than those other systems. A lot of European democracies are younger than the US, and some of them are more frequently deadlocked. I think effectiveness and sustainability are orthogonal concepts here (some would say they are diametrically opposed...)