Text

Art 2. ...
.... The Convention shall also apply to all cases of partial or total occupation of the territory of a High Contracting Party, even if the said occupation meets with no armed resistance.
Commentary

PARAGRAPH 2. -- OCCUPIED TERRITORIES

This new provision is particularly pertinent for the protection of civilian persons under the Fourth Convention, but its inclusion is none the less appropriate in regard to prisoners of war, since, even in the absence of resistance, the Occupying Power might be tempted to intern all or part of the armed forces of the adversary in the interests of its future security. For that reason it was necessary to ensure that such internees would be treated as prisoners of war throughout their detention.
While not expressly mentioned in the Commentary, Art. 2, para 2 has obvious application to a situation where two factions (each claiming to be the legitimate government of a "High Contracting Party", assuming the nation in question previously adopted the Convention) are fighting over that nation's territory. In that case, only one of them can be the legitimate government (and representative of the "High Contracting Party") of the nation. The other faction would be covered as a "Power" to the conflict by Art. 2, para 3.

The situation would be altered factually (and somewhat legally) if one of the factions claimed that it was forming a new nation (state). In that case, the other faction would continue as representative of the "High Contracting Party", and the "new nation" faction would still be covered as a "Power" to the conflict by Art. 2, para 3.

Afghanistan 9-10-2001 involved either situation 1 or 2. Post 9-11-2001, a number of "High Contracting Parties" entered the picture. Which of them, and for what time frame, was an "Occupying Power" is a mixed question of law and fact.