was formed in 1992 precisely because of the way revenue-sharing was occurring in England at the time, and a handful of big clubs didn't want to share so much with everyone else. Spain's overhauls in recent years have little or nothing to do with the NFL, IMO.
The topic and concept of financial fair play in soccer has been around since at least the 1980s (before the NFL adopted a salary cap in 1994), when I became a serious soccer fan. It wasn't formally adopted by UEFA until 15 years ago, after Russian and Middle Eastern oil money started pouring into a few select clubs, but it was not a new concept.
If any American sports league "deserves" credit for the concept, it would probably be the NBA, which adopted a salary cap back in 1984 (and actually had one for one season back in the 1940s). The NBA was and is much more popular and well-known than the NFL in Europe and most of the world, and the timing of their cap implementation better coincides with when discussions about financial fair play started in soccer.