But that branch of history was originally popularly known in English as the "Spanish guitar". The nomenclature of "classical guitar" came after that.

but aren't all guitars descendants of early gut strung guitars, which descended from other instruments like the vihuela or renaissance guitar, etc? in other words, this whole forum could be considered a "classical guitar forum" (or even oud forum) if the umbrella is made big enough.

It's now retrospectively referred to as the classical guitar, so when, etymologically the term was introduced is not as important, the current usage refers back to even mid 18th century guitar playing as classical guitar - Sor, Guiliani, Llobet, and so on. These are referred to today as classical guitarists and the instrument they played as the classical guitar.
Sor - 1778 - 1839 is inarguably referred to today as a classical guitarist playing a classical guitar.

Sor published his Methode pour La Guitare in 1830. It was translated to English in 1832 as Method for the Spanish Guitar. As noted in the Wikipedia writeup, The English edition is a translation from the original in French made by A. Merrick, the organist of Cirencester, and published in London by Cocks & Co. probably in 1832, as "Method for the Spanish Guitar". It is interesting that the French and German versions do not carry the word "Spanish" in the title. This version is today available from Brian Jeffery's Tecla Editions.

Brian Jeffery mentions: "Later in the century, in 1897, Frank Mott Harrison published in London a "Method for the Guitar" by Ferdinando Sor, a work of small value which says (of course wrongly) that the original was written in Spanish."

In any case, whether the English translation meant to imply that the original was in Spanish or referred to the "Spanish" guitar, the fact is that the name of the guitar of that period is now referred to in English as the Classical guitar, not the Spanish guitar, in contemporary usage.

There is a long history of wire-strung instruments as well. Orpharion, bandora, cittern, and some others. Possibly, some instruments thought to be strung with gut were actually strung with wire, wire overwrap or a combination. See http://www.lutesandguitars.co.uk/htm/cat05.htm

isn't that site grand? really beautiful instruments. the one time i spoke to stephen i told him that sometimes i like to go to his site and just look at all the instruments, and it made me feel better about the world. he laughed (but in a nice way).