Just note that this is a 25-year-old thread, resurrected by a new poster today. 
No eres el unico
(Your are not the only one)
I asked about the EEUU thing when I was about seven or so, and my dad told me that it was because plural entities got repeated initials, an United State (Estado Unido) would be EU, but United StateS are EEUU.
I’ve taken that as gospel since then and I think it’s correct.
It’s just like how “page” is abbreviated “p.”, while “pages” is abbreviated “pp.”.
Also, Bienvenido al Straight Dope!
(Scoff.) Anyone can post in 2026 now. If you want to impress us, post in 2026 in 2001.
Not E.E.U.U. but EE.UU. The double E means plural for Estados (States), the double U means plural for Unidos (United). It is a common way to put together abreviations. For instance there is a historic Trade Union called Comisiones Obreras in Spain, that is abreviated CC.OO.
Please note that the English wikiarticle has the abreviation wrong: they messed up the dots.
It is older than me. And older than this thread.
You don’t put the right dots in the correct place in Argentina? Barbarians 
In Spain we sometimes don’t either, but I am a pedant for punctuation.
Nah we do, I’m just lazy and didn’t want to check where the dot went.
[Moderating]
Hello and welcome to the Straight Dope. Note that, while we do not have a rule against bumping very old threads, we ask that users only do so when they have something substantive and new to add. Since this question was already resolved, and since you didn’t add anything new to it, I’ll close it.
But feel free to join in on any current discussions.