My understanding is that medieval warfare, among the noble class, had similarities to this: specifically, nobles didn't necessarily fight to the death. Capture and ransom was a big thing. The term "parole" comes from the idea of giving one's word, after capture, that you would not return to fighting if you were released. The nobles of Europe, too, had an extended network of kin, some of whom might be on the "other side."

I don't recall learning about switching sides with fluidity (as in Afghanistan), but I do recall learning that this little game got broken up once the common people were enlisted.