What American math curriculum? Every American state has its own curriculum and every school district has very broad autonomy, right? I’m no expert but most states don’t even have state exams at the end of high school that are exactly comparable. There are many states that have more internal variety in their education system than most European nations.
The closest the US comes to having a national curriculum is the College Board Exams.
This has changed with Common Core and the pushing of standardized testing to the lower levels (elementary and middle school), though high schools still tend to have more variation.
The closest the US comes to having a national curriculum is the College Board Exams.