The Death of Henry V and the Onset of Civil War in the Holy Roman Empire (1125–1127 CE)

On May 23, 1125, Holy Roman Emperor Henry V died childless, ending the direct Salian dynasty. His widow, Matilda, returned to England, where she would later play a crucial role in the English succession crisis as Empress Matilda, claimant to the English throne.

With no direct heir, the German princes rejected Henry V’s designated successor, his nephew Frederick II, Duke of Swabia, instead electing Lothair II (also called Lothair III), Duke of Saxony, as King of the Romans.

This decision was highly controversial and led to civil war between Lothair’s supporters and the rival Hohenstaufen faction, which claimed the throne for Conrad, Duke of Franconia, nephew of the late emperor.

The Election of Lothair II and the Hohenstaufen Challenge (1125–1127)

• Lothair II had led the opposition against Henry V, making him the preferred candidate of the anti-Salian nobles.
• However, Henry V’s Hohenstaufen nephews, Frederick II of Swabia and Conrad of Franconia, refused to accept Lothair’s rule.
• In 1127, Conrad was elected as a rival King of the Romans, plunging the empire into a civil war between the Hohenstaufen supporters and the loyalists of Lothair II.

Lothair’s Alliance with the Welfs: The Marriage of Gertrude (1127)

To consolidate his power, Lothair strengthened his alliance with the Welf dynasty, which had long been a counterbalance to the Hohenstaufens:

• In 1127, Lothair arranged the marriage of his daughter Gertrude to Henry X ("the Proud"), Duke of Bavaria, a powerful Welf leader.
• As part of this dynastic alliance, Lothair granted Henry X extensive lands in Saxony and Italy, further strengthening Welf influence.

The Inauguration of Civil War

With two rival kings claiming the imperial throne, the Holy Roman Empire descended into civil war:

• Lothair II, backed by the Saxons and Welfs, sought to consolidate his position through strategic alliances.
• The Hohenstaufen faction, led by Conrad of Franconia and Frederick of Swabia, resisted Lothair’s rule and contested his legitimacy.

This conflict would shape German politics for decades, cementing the long-standing rivalry between the Hohenstaufens and Welfs—a struggle that would ultimately influence the broader power struggles of medieval Europe.