The town is linked by a regular train to Cartagena which allows views of the past industrial heritage of the area (lead, alum and silver mining) and the more modern occupations of agriculture and tourism.

The rich mines of La Union provided most of the silver and lead needed by the Late Roman Republic, as it was studied by the archaeologist Eulalia Sintas Martínez.

[10] In this municipality ceramic pots originating from Hellenic civilization were discovered in the archaeological site of Cabezo Agudo.

During the period of Carthaginian control in no little part of the Iberian Peninsula, these people found mining resources in the area of this current municipality.

The Romans conquered Kart-Hadast (the current city of Cartagena in Spain) in the year 209 BC and established in this area.

[11] After the Roman Hispania period and in the era of the arrival and presence of the Visigoths in Murcia, there was a decline in the littoral of Campo de Cartagena.

[12] After this period of the Reconquista, after the Treaty of Alcaraz, and after Alfonso X of Castile had established the Kingdom of Murcia, the mining in La Unión became more relevant.

The property and the usufruct of some mines were allowed only to the monarchs of the Crown of Castile, but they could be awarded to individuals with the payment of fees.

[4] In the year 1527, the emperor Charles V conceded Francisco de los Cobos a permit for utilising the metals of the municipality of Cartagena, to which La unión used to belong.

There are some documentary sources about the Sierra minera of Cartagena and La Unión (a mountain range in both current municipalities).

King Philippe II of Spain signed an order which awards Felipe del Río permission to extract silver and lead.

This increase in inhabitants had its origin in the waves of immigration coming from Andalusia whose people settled in the areas in Región de Murcia where there were more mining activities.

[13] On 1 January 1860, La Unión, Roche and Portmán were conceded a town council, in that time its name was Villa El Garbanzal.

Concrete cases are the constructions of la Casa del Piñón, the building for the public market (antiguo Mercado Público) and the church of El Rosario.

[13] 18.1% of the territory is utilised as croplands in 2019[14] and the most widely grown products are the celeries, the lettuces, the potatoes, the melons and the citrus.