Etymology of 'pre-emptive'

Solution 1:

emption (n.) late 15c., "purchase," from Latin emptionem (nominative emptio) "a buying, purchasing; thing bought," noun of action from past participle stem of emere "to buy"

Originally used to describe something being offered for purchase to a group or individual before being offered publicly.

Solution 2:

"Pre-emptive," as we know it, seems to come from the Latin verb emption-, emptio, from emptus (past participle of emere to buy). See the definition here.

The wikipedia entry of Pre-emption right states that this usage comes from "A right to acquire existing property in preference to any other person... usually referred to as a right of first refusal." It seems as though "pre-emptive" began as just meaning "right to first refusal" and morphed into a more general "right to first action" as time went on.