to introduce him to plans to depose Wallenstein. Initially skeptical of the plans, he unsuccessfully tried to change Wallenstein's mind. He was made provisional supreme commander until the Emperor's son Ferdinand of Hungary took command. After he was informed of the Emperor's decision to arrest or kill Wallenstein, Gallas left the army's headquarters in Pilsen on 12 February 1634 to plan the execution. He declared the orders of Wallenstein, Adam Erdmann Trčka von Lípa and Christian von Ilow invalid and secured the loyalty of the troops while Wallenstein fled to Eger where he was assassinated. Gallas was greatly rewarded with the vast majority of the former Duchy of Friedland. Generalleutnant and Imperial commander In ​the next campaign, Gallas was the actual commander as chief advisor to the inexperienced Ferdinand of Hungary. Their plan was to regain Regensburg and to link up with a Spanish army under the Cardinal-Infante. The Imperials captured Regensburg on 26 July, followed by Donauwörth on 16 August. They proceeded to besiege Nördlingen where the Spanish army joined their forces. A numerically inferior Swedish force under Gustav Horn and Bernhard of Saxe-Weimar tried to lift the siege and attacked them on 5 September but Gallas directed the united Habsburg army to a resounding victory in the Battle of Nördlingen. The Swedes lost two armies and the control over southern Germany while the Imperials chased them up to the Main before moving into winter quarters in Württemberg. The attention of the Imperials turned to the Rhine in 1635. After the open outbreak of hostilities with France, Gallas and his troops crossed the river at the recently captured Philippsburg in May. He captured most of the Palatinate with Kaiserslautern as well as Worms and started to besiege Mainz in summer. At the approach of a French-Weimar relief force under Bernhard and Cardinal La Valette, Gallas retreated to harass them with light cavalry and to cut off their supplies. This proved successful, most of the French army perished because of sickness or hunger, or it dissolved on its retreat to Metz. The siege of Mainz was renewed and successfully concluded in December while Gallas advanced via Saarbrücken into Lorraine. He joined forces at Dieuze with the exiled Duke of Lorraine who urged to recapture his capital Nancy. Yet Gallas preferred to entrench his army at the Seille to give his troops some rest. An outbreak of the plague and shortage