There was an attempt in 1498 to unite all Iberia under one personal union into a super Spain, under Miguel Da Paz, heir to Portugal, Castile and Leon, which he would get from Grandpa and Grandma Ferdinand and Isabella. Unfortunately, he died at age two, and the idea of all hispania being united died Except for that bit But what if, instead of the king of spain inheriting a portuguese empire, it was a united kingdom within spain from the beginning?