2. The Germanic Tribes in the West

The great waves of barbarian invasions, also known as invasions of the Germanic tribes, took place over the course of several centuries (from 1st to 5th). In 376, the Goths, which were a union of very diverse peoples, reached an agreement with the Roman Emperor Valens: he will give them land to live within the Empire, but they will have to work on farms and as auxiliary troops, since Valens was preparing an attack against the Sassanid Persians.
However, the Romans did not fulfill the land promises they made to the Goths and they rebelled. In 378 the Battle of Adrianople took place, in which Goths, Alans and Huns completely defeated the army of Rome. Emperor Valens himself died in battle. From this moment on, the Goths will never leave the Roman Empire.

There were very different tribes or peoples (Franks, Visigoths, Ostrogoths, Lombards, Saoxons, Angles, etc.) but for the Romans they were all practically the same, hence they called them all barbarians, which means something like "foreigner", in the sense of uncivilized.
They arrived from northern Europe and took advantage of the weakness of the last years of the Western Roman Empire to penetrate their territories. Uncapable to confront the invaders in the Iberian Peninsula (Swabians, Vandals and Alans), the Western Roman Empire had to hire mercenaries for their army among the warriors of another Germanic tribe, the Visigoths. These were fearsome warriors who had even sacked the city of Rome itself in 410, since their leader, Alaric, wanted to be named general of Rome, but the senators were not up to the task.

It's funny how many of these invading people wanted to be part of the famous Roman Empire, even despite the Romans themselves, who suffered the continuous invasions firsthand. Although this mercenary army worked at the beginning and Vandals and Alans were expelled, we will see that, in the long run, it was a bad idea, since the Visigoths settled definitively in Hispania, although perhaps Rome had no other alternative.

The Visigoths had their capital in Toulouse, France, but the Franks, who were their enemies, conquered all that area and the Visigoths had no choice but to move their capital southwards to Toledo in 576, under king Leovigild.
Like the rest of the Germanic peoples, they were basically engaged in agriculture and war, with little intellectual concern. The monasteries were the only institutions that preserved the culture of antiquity.
The Visigothic kings did not inherit the throne, but the monarch was chosen by the most prestigious warriors. This caused many civil wars and the instability of the kingdom.

Besides, there was a serious problem: it was difficult to integrate the native Hispano-Roman population, since this was Catholic, while the Visigoths were Arians. Finally, in 589, a Council was held in Toledo in which the King Recaredo converted to Catholicism to avoid further religious conflicts. Now the kingdom was more unified. Later, in 623, King Suintila definitively expelled the Byzantines from the south of the Peninsula.
In 654, the unification of the kingdom took a further step with the publication of the Liber Iudiciorum, a compendium of laws, by King Recceswinth.
However, it was not enough to avoid the continuous civil wars that occurred over succession to the throne. This meant that the monarchies were weak and the armies were divided, which was used by the Moors from North Africa to invade Spain in 711 (Battle of Guadalete). That was the end of the Visigoth kingdom.