Reddit reviews Scipio Africanus: Rome's Greatest General

De Bello Gallico is a great primary text. Scipio Africanus: Rome’s Greatest General is a nice read too

This wasn't really an event that happened all at once, so while I'm sure there's books specifically about the Romans in Spain, it may be easier to look at the individual events. It really depends how in-depth you want to go. While there was native tribes the real base of power early on was the trading colonies on the southern and eastern coasts established by the Phoenicians and later the Carthaginians, this collection of essays discusses the culture and early settlement of Iberia. After their defeat in the First Punic War, mainly to recoup losses, Hannibal Barca of Carthage began the actual conquest of southern Spain. This is relevant because this was Hannibal's base of departure, which by that point had been extended farther north up the coast, in his campaigns against Rome, and probably Scipio Africanus's most important annexation after Hannibal's defeat. There are so many books on the Second Punic War, I'm sure an index search for Iberia would be helpful. There are many standard books for that, I would look for the cheapest, but maybe be sure that it is not emphasizing only Hannibal in its contents as many books will, if you want info on the actual campaigns in Iberia look up Scipio Africanus's Iberian Campaign, here's a book I know talks about it. Even the wikipedia article, while not a legitimate source to cite, has a massive description of it in this article so you'd get the gist.

After this point, it was essentially a many-centuries long process of resistance against Rome by initially the Carthaginians, and then the natives who were focused more inland, and gradual Roman conquest of the entire peninsula westward to Lusitania, or modern-day Portugal. This is the point where I don't really know any specific books, though you could search individually or simple for "Roman wars in iberia", because there were many many wars with individual tribes, and a continual strong Roman military presence in Iberia, or what we should really be calling Hispania as the romans would. This is all during the Roman republic though, and the final phase of the conquests at the beginning of the Empire is a bit more famous because it involved the fiercely independent, both culturally and politically to this day, peoples that populated the hills and forests of northern Spain, Asturia and Cantabria. It would be the same reasons that the Romans had such a hard time conquering this area, that the Muslims caliphates would later also have a hard time, and this area would actually become the birthplace of the reconquista. I also don't know any sources specific to this, but they are often included in sources about the reign and specifically military campaigns under Augustus, the first Emperor of Rome. Good luck, let me know if you need tips on source-searching