[1] In June 1572, Spanish conquistadors led by Juan de Salcedo arrived in the Ilocos Region to subdue the native people and pacify the area.

On October 1849, Governor-General Narciso Clavería issued a decree that led to the creation of La Union province, formed by merging towns from Ilocos Sur, Pangasinan, and the eastern part of the País del Igorrotes (now the Cordillera region).

[2][3] Historically, the coastal areas of the Ilocos Region were frequent targets of raids by Moro and Chinese pirates, who looted villages (barrios) and captured women and children for enslavement.

[2] One notable encounter occurred on October 8, 1846, when Moro pirates landed on the northern shores of Pangasinan, specifically in Bauang, due to adverse weather conditions.

[2] The local gobernadorcillo (town mayor) organized a defense, resulting in a bloody clash in which the Christians killed four Moros, captured 29 prisoners, and seized a warship armed with four cannons.

[2] The 6- to 7-meter-high circular adobe watchtowers (baluartes), constructed mainly from coral blocks and held together by lime and egg whites, stand as historical monuments to the vigilance of these communities against potential attacks.

[2] During the American colonial period and the Japanese occupation of the Philippines in World War II, the watchtowers of La Union were repurposed as military installations for monitoring potential threats along the coastline, such as enemy ships or aircraft.