Why do we say Iraq War but not Afghanistan War?

Not another debate over the rights and wrongs of those wars but a peculiar linguistic quirk pointed out by Jay Nordlinger

My colleague and I were talking about this, too: We say “Iraq War”; but “Afghan War.” Those are unequal. We would never say “Iraqi War” or “Afghanistan War.” Strange.
We refer to the “Korean War.” But we would never say “Vietnamese War.” We say “Vietnam War” — and not “Korea War.”
It is curious. My theory is that we instinctively reach for the adjective but collectively abandon this rule for multi-syllable countries. So 'Korean' but not 'Vietnamese'.

Not very scientific but when did that stop me ....