They came in tall ships, with golden hair and sparkling eyes. They came wielding magic as easy as they breathed. They came. And they conquered.
Elves in Weyland are not natives, they are descendants of the explorers and conquerors who arrived at the continent some 900 years prior to the present day. Here, in the south, they razed entire civilizations, enslaving the native humans in their quest for gold and magic. In the north, elves arrived later, building a relationship with the native humans that culminated in the Kingdom of Gilead.
The southern elves are better known as The Elves of Cadiz. What, exactly, Cadiz means no one seems to know (or the elves aren't telling). Most believe Cadiz refers to the great elvish homeland across the ocean, but there is some debate about that. Granted, elves leave in ships and never return, but no non-elf has ever seen the elvish homeland. The Elves of Cadiz correspond to the "High Elf" subrace in the D&D Basic Rules, with all the associated bonuses and proficiencies. For a historical analogue, think 16th Century Spain. They tend to be fierce warriors, cunning wizards, or fanatical clerics.
The Elves of Cadiz are quasi-monotheistic, worshiping Jad.
Jad is personified by the sun, which features prominently in the church's iconography. The Jaddite Church is theologically large and sprawling, with sects devoted to certain aspects of the sun (like dawn or dusk) or venerating past heroes or kings like saints. Initial forays into the area that became Weyland were largely church affiliated, which resulted in many missions dotting the Barony. Many of these are now abandoned as the influence of the elves has waned, yet most humans in Weyland ostensibly belong to the Church of Jad.
The Cadizian Elves feel Weyland is theirs and have tried numerous times to retake it. They have been stopped by the native humans and dwarves, together with the forces of Gilead. Many Cadizian elves still live in the barony, some openly armed and advocating independence or a return of elvish rule.
Influences -- Spanish history (especially their conquest of Mexico), Texas history, Pelor from various incarnations of D&D, The Lions of al-Rasan by Guy Gavriel Kay, Tolkien