The Carolingians were once a great house. Their glory began with Charles Martel, who was merely a “Mayor of the Palace” - although he did de facto rule over the Franks. He was faced with a Muslim invasion, although some modern historians consider it more of a raid. The Muslims would conquer much of Aquitaine, and its duke requested aid, although he had previously revolted against the Franks.
Charles accepted this request for aid. He met the Muslims at Tours, and their commander was killed. Without a commander, the Muslim raiding force quickly withdrew. For this feat, Charles was known as “Martel” - the Hammer.
His heirs were Peppin and Carloman. They quickly managed to assert effective control over Francia. Carloman ruled Austrasia, Alemannia, and Thuringia (the eastern portions of the Frankish realm), whereas Peppin ruled Neustria, Burgundy, and Provence (the western portions of Francia). They would install Childeric III as a puppet king of the Franks, although they retained all of the actual power.
Carloman would retire into religious life in 747 AD. Peppin would thus effectively rule over the entire Frankish realm. He would suppress a revolt by his half-brother. In 751 AD, he gave up all pretence of non-monarchical rule, as he forced Childeric into a monastery.
Peppin’s sons would divide the realm, but convenient deaths would lead to the ascension of Charles to the position of King of all Francia. Charles would then defeat the Saxons, Muslims, and Lombards alike. These deeds earned him the title “Magnus” - the Great.
The man known as Charlemagne also gave land to the Pope to rule, who crowned him as Western Roman Emperor in 800 AD.
Ultimately, though, Charlemagne was a mortal man, and he would perish. His son, Louis the Pious, would inherit. Unfortunately, Louis would be the last ruler of a united Empire. His sons would fight over the crown.
In the end, the Treaty of Verdun would divide the realm into 3 parts. To make matters worse, when the eldest son, Lothaire, died, he split his realm into 3 parts - Italy, Lotharingia, and Arles (Burgundy).
In time, all of the Carolingians would lose their authority. Lotharingia was the first realm to be destroyed, and that kingdom was heavily fought over by East and West Francia. By 1066 AD, the Carolingians had been reduced to a single county in the former lands of West Francia, now known as France.
Meanwhile, the King of East Francia (known as Germany by that point), Otto, would conquer Italy in the 900s AD and have himself crowned as Holy Roman Emperor.
Count Herbert of Vermandois, however, dreamed of restoring Carolingian glory. His ambitions would lead to countless wars and intrigues, and that is the true history of the restored Carolingians and their descendants.