Louis was born in Chasseneuil-du-Poitou in the year 778 to Charlemagne and Hildegarde. Following Charlemagne's war with Aquitaine, he placed Louis in charge of the subkingdom in the year 781 with regnants. As he grew up in Aquitaine, he learned how to rule a kingdom and fight in wars, though he was known for being very devout and loyal to the Christian Church, ergo the nickname 'Pious'.
As he aged and made decisions for himself as king, he was placed in charge of more things. When Charlemagne invaded Barcelona, Louis was placed in charge of the area until it was retaken by the Umayyad Caliphate. In order to take it back, he besieged the city for two years until it finally surrendered.
In accordance with Frankish tradition, Charlemagne had prepared to split his kingdom among his sons before he died. Many of them, however, died before Charlemagne had. By the time Charlemagne had died, his only remaining sons were Louis I and Pepin.
Charlemagne appointed Louis as co-emperor before his death due to his declining health. Upon his death in 814, the kingdom was split between the Byzantine and Frankish Empires. Louis became the sole emperor of the Franks while his brother, Pepin, ruled the Byzantines. Immediately, Louis was in charge of the Frankish Empire in the midst of the Unification Wars.
Louis initially joined the Frankish forces on the front lines, though an injury to the leg suffered during an assassination attempt in an ambush. The wound was infected and Louis was bed-ridden for some time before he recovered. After his injury, Louis led the war from behind the scenes rather than in person. Despite this, Louis the Pious was said to have been a cunning tactician, especially during the course of this war. Without his leadership, the Frankish armies were likely to have faltered.
Dealing with the Unification Wars occupied a large chunk of his rule. It wasn't until 831, six years before Louis' death, that the war ended and Louis was able to enjoy relative peace in the empire.
Uniting the Carolingian Union
Despite his leadership during the Unification War, Louis is most remembered, along with his brother, for helping to unite the Byzantine and Frankish Empires. During and after the war, dissent between the two nations had grown severe. Troop desertion, mistreatment of civilians, and rebellions grew rampant, especially in the 820s.
Louis had been crowned Holy Roman Emperor in 816, an unexpected move by the pope. Many people assumed Pepin of Italy would receive the honor due to his assistance to the Pope in the past. However, Louis was crowned Holy Roman Emperor allegedly due to his kingdom's proximity to Rome as opposed to the Byzantine Empire's proximity to Rome. Nevertheless, the Byzantines were upset by this. Pepin of Italy helped quell the protests regarding this move.
In order to bring the two people together, the brothers worked on creating more acts that would bring the two empires together. The upper classes of both nations were already on good terms with each other. These warm feelings were supposed to have bled down into the lower classes. This was the case in larger cities and wealthy cities, though remote cities and towns were still opposed to the Byzantines.
The two didn't run into distinct problems until 821, when several villages and towns in Saxony rebelled. The rebellions were quickly put down, but it inspired a wave of rebellions in the area throughout the decade. Pepin also had to put down several rebellions in the Byzantine Empire. Ultimately, the relations between the two nations had improved to a considerable point by 840. While remote areas still had dissenting views, areas along trade routes, along with populated cities and coastal cities, viewed the Byzantines more as brothers than enemies.
Louis also assisted in repairing religious squabbles between the eastern Europe and western Europe. His actions are said to have prevented a schism in the Church and aided the Franks and Byzantines in further uniting culturally under the Carolingian Union.
Louis' injuries from the Unification Wars affected him for the rest of his life. He was known to have walked with a severe limp, which became more pronounced in his later years. On 12 October 837, during a tour of Aachen with several nobles, he fell down the stairs of the Palace of Aachen. These injuries proved to be fatal and he died in his sleep on 14 October 837. His son, Lothair I, became King of the Franks.
Louis is remembered in mixed views. While many people credit him with unifying the Franks and Byzantines, many people believe that Francia itself suffered due to Louis being more concerned with the Unification Wars and relations with the Byzantines than what was happening in his own kingdom. Regarding his actions during the rebellions of 820, he is criticized for neglecting the growing situation and waiting until the last minute to act. Still, he is remembered for also helping to end the rebellions. His inaction with Frankish affairs so he could focus on Byzantine-Frankish relations, however, is remembered today as 'necessary'.