The Celts are believed to have been the first inhabitants of Germany. They were followed by German tribes at the end of the 2nd century German invasions destroyed the declining Roman Empire in the 4th and 5th centuries One of the tribes, the Franks, attained supremacy in western Europe under Charlemagne, who was crowned Holy Roman Emperor in 800. By the Treaty of Verdun (843), Charlemagne's lands east of the Rhine were ceded to the German Prince Louis. Additional territory acquired by the Treaty of Mersen (870) gave Germany approximately the area it maintained throughout the Middle Ages. For several centuries after Otto the Great was crowned king in 936, German rulers were also usually heads of the Holy Roman Empire.
By the 14th century, the Holy Roman Empire was little more than a loose federation of the German princes who elected the Holy Roman Emperor. In 1438, Albert of Hapsburg became emperor, and for the next several centuries the Hapsburg line ruled the Holy Roman Empire until its decline in 1806. Relations between state and church were changed by the Reformation, which began with Martin Luther's 95 theses, and came to a head in 1547, when Charles V scattered the forces of the Protestant League at Mühlberg. The Counter-Reformation followed. A dispute over the succession to the Bohemian throne brought on the Thirty Years' War (1618–1648), which devastated Germany and left the empire divided into hundreds of small principalities virtually independent of the emperor.
After the fall of the Western Roman Empire, the Franks created an empire under theMerovingian kings and subjugated the other Germanic tribes. The Merovingian kings of the Germanic Franks conquered northern Gaul in 486 AD. Swabia became a duchy under the Frankish Empire in 496, following theBattle of Tolbiac; in 530 Saxons and Franks destroyed the Kingdom of Thuringia. In the 5th and 6th centuries the Merovingian kings conquered several other Germanic tribes and kingdoms. King Chlothar I(558–561) ruled the greater part of what is now Germany and made expeditions intoSaxony, while the Southeast of modern Germany was still under influence of the Ostrogoths. Saxons inhabited the area down to the Unstrut River.
Regions of the Frankish Empire were placed under the control of autonomous dukes of mixed Frankish and native blood. Frankish Colonists were encouraged to move to the newly conquered territories. While the local Germanic tribes were allowed to preserve their laws, they were pressured into becoming Christians.
The German territories became part of Austrasia (meaning "eastern land"), the northeastern portion of the Kingdom of the Merovingian Franks. As a whole, Austrasia comprised parts of present day France,Germany, Belgium, Luxembourg and the Netherlands. After the death of the Frankish king Clovis I in 511, his four sons partitioned his kingdom including Austrasia. Authority over Austrasia passed back and forth from autonomy to kingly subjugation, as Frankish lands were alternately united and subdivided by the Merovingiankings.
In 718, Charles Martel, the Franconian Mayor of the Palace, made war against Saxony because of its help for the Neustrians. His son Carloman started a new war against Saxony in 743, because the Saxons gave aid to Duke Odilo of Bavaria.
In 751 Pippin III, Mayor of the Palace under the Merovingian king, himself assumed the title of king and was anointed by the Church. Now the Frankish kings were set up as protectors of the pope, and Charles the Greatlaunched a decades-long military campaign against their heathen rivals, the Saxons and the Avars. The campaigns and insurrections of the Saxon Wars lasted from 772 to 804. The Saxons and Avars were eventually overwhelmed, the people were forcibly converted to Christianity, and the lands were annexed by the Carolingian Empire.
Otto the Great
In 936, Otto I the Great was crowned as king at Aachen; his coronation as emperor by the Pope at Rome in 962 inaugurated what became later known as the Holy Roman Empire (The Holy Roman Empire was a multi-ethnic complex of territories in central Europe that lasted from the coronation of Otto I as emperor in 962 until Francis IIdissolved the imperial title in 1806. The largest territory and core of the empire was the Kingdom of Germany, and at its peak the empire included theKingdom of Italy, the Kingdom of Bohemia and theKingdom of Burgundy), which became to be identified with Germany.Otto strengthened the royal authority by re-asserting the old Carolingian rights over ecclesiastical appointments. Otto wrested from the nobles the powers of appointment of the bishops and abbots, who controlled large land holdings. Additionally, Otto revived the old Carolingian program of appointing missionaries in the border lands. Otto continued to support celibacy for the higher clergy, so ecclesiastical appointments never became hereditary. By granting land to the abbotts and bishops he appointed, Otto actually made these bishops into "princes of the Empire" (Reichsfürsten); in this way, Otto was able to establish a national church. Outside threats to the kingdom were contained with the decisive defeat of the Hungarian Magyars at the Battle of Lechfeldin 955. The Slavs between the Elbe and the Oder rivers were also subjugated. Otto marched on Rome and droveJohn XII from the papal throne and for years controlled the election of the pope, setting a firm precedent for imperial control of the papacy for years to come.
During the reign of Conrad II's son, Henry III (1039 to 1056), the empire supported the Cluniac reforms of the Church – the Peace of God, prohibition of simony (the purchase of clerical offices), and required celibacy of priests. Imperial authority over the Pope reached its peak. In the Investiture Controversy which began between Henry IV and Pope Gregory VII over appointments to ecclesiastical offices, the emperor was compelled to submit to the Pope at Canossa in 1077, after having been excommunicated. In 1122 a temporary reconciliation was reached between Henry V and the Pope with the Concordat of Worms. The consequences of the investiture dispute were a weakening of the Ottonian church (Reichskirche), and a strengthening of the Imperial seular princes
The time between 1096 and 1291 was the age of the crusades. Knightly religious orders were established, including the Knights Templar, the Knights of St John (Knights Hospitaller), and the Teutonic Order.
The term sacrum imperium (Holy Empire) was first used under Friedrich I, documented first in 1157.
Long-distance trade in the Baltic intensified, as the major trading towns became drawn together in the Hanseatic League, under the leadership ofLübeck. The Hanseatic League was a business alliance of trading cities and their guilds that dominated trade along the coast of Northern Europe. Each of the Hanseatic cities had its own legal system and a degree of political autonomy. The chief cities were Cologne on the Rhine River, Hamburg and Bremen on theNorth Sea, and Lübeck on the Baltic. The League flourished from 1200 to 1500, and continued with lesser importance after that.
The German colonisation and the chartering of new towns and villages began into largely Slav-inhabited territories east of the Elbe, such as Bohemia, Silesia, Pomerania, and Livonia. Beginning in 1226, theTeutonic Knights began their conquest of Prussia. The native Baltic Prussians were conquered and Christianized by the Knights with much warfare, and numerous German towns were established along the eastern shore of the Baltic Sea.