> Amnesty International says they just threw huge numbers in prison without any due process
Due process just means... process that is due. But (for better or for worse, depending on how you view this) it could totally be the case that nothing was due in the particular situation, at least legally. Since people look at this from a USA angle, here's the US constitution:
"The Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it."
Notice that in the scenario described, a right such as habeas corpus simply isn't due. You can't be violating due process if there was no process due.
Notice this isn't pedantry; national security has always been something states have at least partially prioritized over individual rights. I make no judgment of the morals of the situation, but I thought it was worth pointing out that rights aren't as absolute (legally, anyway) as people think they are.