Due process and judicial process in a courtroom are not the same thing. Your citizenship isn't a bubble you carry around with you that gives you enhanced protection from your government under all circumstances; if you choose to put yourself in a kinetic theater of operations then it doesn't act as a bullet proof vest.

In the case of Al-Awlaki, his due process was people in the executive branch (specifically the National Security Council) looking at the fact that he was running around on battlefields with people the US was fighting with, and deciding that he'd chosen to become an enemy combatant. You can certainly critique the general conduct of war by states, and whether the US should be engaged in asymmetric wars in general or in that theater in particular, but I am no more or less exercised about al-Awlaki's death than I am about any of his Yemeni/Al Qaeda associates that were blown up at the same time.

Put another way, if you were OK with them being killed, then you should be OK with him being killed because he chose to affiliate with them. If you're not OK with it, then I'd say the problem is the War on Terror as a whole, since it effectively functions as a blank check to target any group that can be designated as a military threat.

Not off the top of my head, but the Supreme Court decision in Ex Parte Quirin, From WWII, makes entirely clear that enemy combatants who are US citizens are not entitled to special treatment as compared to enemy combatants who are not citizens.

> There is supposed to be a strict separation of never using the military against the citizens of the united states

There is no legal or historical basis for this claim; in fact, the Constitution explicitly envisions the use of military force to suppress insurrection, which is ordinarily carried out by civilians; it is clearly intended that the government not act extrajudicially against persons (not just civilians) within the jurisdiction of the US when access to the civilians justice system is available, but enemy combatants, regardless of citizenship, at least when outside the practical reach of the US civilian justice system, don't seem to have any protection from the application of military power at any time in history.

Most of the people targeted, individually or generally, by the US military in the Civil War were US citizens, for instance.

Next given the scale of wwii I’m sure there were us citizens fighting for the axis powers. The main difference is we lacked the ability to track, research, and target individuals like we do today.

alleged criminals are killed on the streets almost every day. From legal standpoint, what is difference between them and terrorists in your opinion?