A stem duchy (German: Stammesherzogtum, from Stamm, meaning "tribe", in reference to the Germanic tribes of the Franks, Saxons, Bavarians and Swabians) was a constituent duchy of the Kingdom of Germany at the time of the extinction of the Carolingian dynasty (the death of Louis the Child in 911) and through the transitional period leading to the formation of the Holy Roman Empire later in the 10th century. The Carolingians had dissolved the original tribal duchies of the Frankish Empire in the 8th century. As the Carolingian Empire declined in the late 9th century, the old tribal areas assumed new identities as subdivisions of the realm. These are the five stem duchies (sometimes also called "younger stem duchies" in contrast to the pre-Carolingian tribal duchies): Bavaria, Franconia, Lotharingia, Saxony and Swabia (Alemannia).  The Salian emperors (reigned 1027-1125) retained the stem duchies as the major divisions of Germany, but they became increasingly obsolete during the early high-medieval period under the Hohenstaufen, and Frederick Barbarossa finally abolished them in 1180 by in favour of more numerous territorial duchies.
The term Stammesherzogtum as used in German historiography dates to the mid-19th century, and from the beginning was closely related to the question of national unification. The term's applicability, and the nature of the stem duchies in medieval Germany, consequently have a long history of controversy. The overly literal or etymologizing English translation "stem duchy" was coined in the early 20th century. While later authors tend to clarify the term by using the alternative translation "tribal", use of the term "stem duchies" has become conventional.
The derivation of the German people from a number of German tribes (Deutsche Stämme; Volksstämme) developed in 18th to 19th century German historiography and ethnography. This concept of German "stems" relates to the early and high medieval period and is to be distinguished from the more generic Germanic tribes of Late Antiquity. A distinction was sometimes made between the "ancient stems" (Altstämme), which were in existence in the 10th century, and "recent stems" (Neustämme), which emerged in the high medieval period as a result of eastward expansion. The delineation of the two concepts is necessarily vague, and as a result the concept has a history of political and academic dispute. The terms Stamm, Nation or Volk variously used in modern German historiography reflect the Middle Latin gens, natio or populus of the medieval source material.
Traditional German historiography counts six Altstämme or "ancient stems", viz. Bavarians, Swabians (Alamanni), Franks, Saxons, Frisians and Thuringians. All of these were incorporated in the Carolingian Empire by the late 8th century. Only four of them are represented in the later stem duchies; the former Merovingian duchy of Thuringia was absorbed into Saxony in 908 while the former Frisian kingdom had been conquered into Francia already in 734. The customary or tribal laws of these groups were recorded in the early medieval period (Lex Baiuvariorum, Lex Alamannorum, Lex Salica and Lex Ripuaria, Lex Saxonum, Lex Frisionum and Lex Thuringorum). Franconian, Saxon and Swabian law remained in force and competed with imperial law well into the 13th century.
The list of "recent stems" or Neustämme, is much less definite and subject to considerable variation; groups that have been listed under this heading include the Märker, Lausitzer, Mecklenburger, Upper Saxons, Pomeranians, Silesians, and East Prussians, roughly reflecting German settlement activity during the 12th to 15th centuries.
The use of Stämme, "tribes", rather than Völker "nations, peoples", emerged in the early 19th century in the context of the project of German unification. Karl Friedrich Eichhorn in 1808 still used Deutsche Völker "German nations". Friedrich Christoph Dahlmann in 1815 asked for unity of the German nation (Volk) in its tribes (in seinen Stämmen). This terminology became standard and is reflected in the preamble of the Weimar constitution of 1919, reading Das deutsche Volk, einig in seinen Stämmen [...] "The German nation (people), united in its tribes (stems) ...".
The composition of the German population of these stems or tribes as a historical reality is mostly recognized in contemporary historiography, while the caveat is frequently made that each of them should be treated as an individual case with a different history of ethnogenesis, although some historians have revived the terminology of "peoples" (Völker) rather than "tribes" (Stämme).
The division remains in current use in the conventional classification of German dialects into Franconian, Alemannic, Thuringian, Bavarian and Low Saxon (including Friso-Saxon, with Frisian proper being regarded as a separate language). In the Free State of Bavaria, the division into "Bavarian stems" (bayerische Stämme) remains current for the populations of Altbayern (Bavaria proper), Franconia and Swabia.
Within East Francia were large duchies, sometimes called kingdoms (regna) after their former status, which had a certain level of internal solidarity. Early among these were Saxony and Bavaria, which had been conquered by Charlemagne, and Alamannia, placed under Frankish administration in 746. In German historiography they are called the jüngere Stammesherzogtümer, or "more recent tribal duchies", although the term "stem duchies" is common in English. The duchies are often called "younger" (newer, more recent, etc.) in order to distinguish them from the older duchies which were vassal-states of the Merovingian monarchs. Historian Herwig Wolfram denied any real distinction between older and younger stem duchies, or between the stem duchies of Germany and similar territorial principalities in other parts of the Carolingian empire:
I am attempting to refute the whole hallowed doctrine of the difference between the beginnings of the West-Frankish, "French", principautés territoriales, and the East-Frankish, "German," stem-duchies. . . Certainly, their names had already appeared during the Migrations. Yet, their political institutional, and biological structures had more often than not thoroughly changed. I have, moreover, refuted the basic difference between the so-called älteres Stammesfürstentum [older tribal principalities] and jüngeres Stammesfürstentum [newer tribal principalities], since I consider the duchies before and after Charlemagne to have been basically the same Frankish institution. . .
After the division of the Kingdom in the Treaties of Verdun (843), Meerssen (870), and Ribemont (880), the Eastern Frankish Kingdom or East Francia was formed out of Bavaria, Alemannia, and Saxony together with eastern parts of the Frankish territory. The kingdom was divided in 864–865 among the sons of Louis the German, largely along the lines of the tribes. Royal power quickly disintegrated after 899 under the rule of Louis the Child, which allowed local magnates to revive the duchies as autonomous entities and rule their tribes under the supreme authority of the King.
After the death of the last Carolingian, Louis the Child, in 911, the stem duchies acknowledged the unity of the kingdom. The dukes gathered and elected Conrad I to be their king. According to Tellenbach's thesis, the dukes created the duchies during Conrad's reign. No duke attempted to set up an independent kingdom. Even after the death of Conrad in 918, when the election of Henry the Fowler was disputed, his rival, Arnulf, Duke of Bavaria, did not establish a separate kingdom but claimed the whole, before being forced by Henry to submit to royal authority. Henry may even have promulgated a law stipulating that the kingdom would thereafter be united. Arnulf continued to rule it like a king even after his submission, but after his death in 937 it was quickly brought under royal control by Henry's son Otto the Great. The Ottonians worked to preserve the duchies as offices of the crown, but by the reign of Henry IV the dukes had made them functionally hereditary.
The five stem duchies were:
The complicated political history of the Holy Roman Empire during Middle Ages led to the division or disestablishemt of most early medieval duchies. Frederick Barbarossa in 1180 abolished the system of stem duchies in favour of more numerous territorial duchies. The duchy of Bavaria is the only stem duchy that made the transition to territorial duchy, eventually emerging as the Free State of Bavaria within modern Germany. Some of the other stem duchies emerged as divisions of the Holy Roman Empire; thus, the Electorate of Saxony, while not directly continuing the duchy of Saxony, gives rise to the modern state of Saxony. The duchies of Franconia and Swabia, on the other hand, disintegrated and correspond only vaguely to the contemporary regions of Swabia and Franconia. The Merovingian duchy of Thuringia did not become a stem duchy of the Holy Roman Empire but was demoted to landgraviate within Saxony in 908, and the modern state of Thuringia was established in 1920.