If a trial isn’t planned to be part of an FDA submission, then technically it doesn’t have to meet those standards. However, 1) pharma companies are constantly trying to standardise the way they work, and 2) sometimes a trial that isn’t originally planned for submission to the FDA has results that can’t be ignored. As a result the vast majority of trials are conducted to FDA standards (or indeed higher, where there are regional regulations that exceed those of the FDA), regardless of whether they are going to be submitted.

The point is that by setting the highest standards, the US government effectively sets the framework worldwide. The only time this would not be true, would be if the EU (or possibly Japan) decided to set higher standards generally, at which point they would be setting the agenda. At the moment they are largely content to take their lead from the FDA.

US is free to reject the clinical trial protocols of another country, and not allow the products for sale in the US. Unless there is a bilateral agreement, such a move will be (rightly) construed as an affront.