Diet of Regensburg (1623)

The Diet of Regensburg of 1623 was a meeting of the Imperial States of the Holy Roman Empire (or Fürstentag) convened by Holy Roman Emperor Ferdinand II. The meeting was not technically an imperial diet in the full sense, but a convention of princes or Deputationstag – a looser constitutional format giving the emperor greater leeway to take decisions without being bound by formal procedures. At it the Electorate of the Palatinate was transferred to Maximilian I of Bavaria. The meeting marked the high-water mark of imperial power during the Thirty Years' War.

Frederick V, Prince-elector of the Rhine Palatinate, had been placed under the imperial ban for his role in the Bohemian Revolt of 1618–1621. His lands on the Rhine had been overrun by the army of Ferdinand's cousin Philip IV of Spain in the Palatinate campaign, and the Bohemian rebels had been defeated at the Battle of the White Mountain by an army led by another of the emperor's cousins, Duke Maximilian of Bavaria. The army of the German Catholic League, commanded by Johann Tserclaes, Count of Tilly, had defeated Frederick's allies Ernst von Mansfeld and Christian of Brunswick at the Battle of Wimpfen (6 May 1622) and Battle of Höchst (20 June 1622). It looked as though the Catholic forces had won the war, and the emperor wished to finalise Frederick's deprivation as elector with the agreement of the leading princes. On 27 July 1622 the emperor called a convention of princes to be held in Regensburg late that year.

...
Wikipedia