The creed recited at Toledo says that the Holy Spirit proceeds from the Father and the Son. The creed agreed at Constantinople in 381 says that the Spirit proceeds from the Father. The added phrase is one word in Latin, filioque, and it became the doctrinal marker of the division between eastern and western Christianity.
In Spain it was not a provocation. It was an anti-Arian reflex. Arianism made the Son less than the Father, so a church that had just spent two centuries arguing against Arianism reached for any formula that tied the Son more tightly into the divine life, and saying the Spirit proceeds from him too does exactly that. Whether Toledo is the first conciliar text to carry the addition is argued by specialists. That Spain is where it took hold is not.
From Spain it travelled to the Frankish church, which adopted it enthusiastically and pressed Rome to do the same. Rome resisted for a long time on the ground that nothing may be added to a creed a council has fixed, whatever its merits, and only accepted it into the Latin creed centuries later. By then it was one of the standing eastern grievances against the west, and it was cited as such in 1054 and at every subsequent attempt at reunion.
The eastern churches have never accepted it. A phrase added at a provincial council to close down a local heresy became, four hundred years later, one of the two or three things that separate half of Christendom from the other half.