That this engagement was not enough, later events were to show. For the present it seemed satisfactory to John George, and Maximilian was able to turn his attention to the actual preparations for war. In May orders had been issued from Madrid to Spinola, the Spanish general in the Netherlands, to make ready to march to the Emperor's defence; and on June 3 the frightened Union signed the treaty of Ulm, by which they promised to observe neutrality towards the League, thus securing to Maximilian freedom from attack in the rear during his march into Bohemia. The Union, however, if it should be attacked, was to be allowed to defend its own territories, including the Palatinate. [Sidenote: § 8. The invasions.] At the head of Maximilian's army was the Walloon Tilly, a man capable of inspiring confidence alike by the probity of his character and by the possession of eminent military capacity. On June 23 he crossed the Austrian frontier. On August 20 the Estates of Upper Austria unconditionally bowed to Ferdinand as their lord and master. Lower Austria had already submitted to its fate. About the same time John George had entered Lusatia, and was besieging Bautzen in Ferdinand's name. Spinola, too, had marched along the Rhine, and had reached Mentz by the end of August. [Sidenote: § 9. Spinola subdues the Western Palatinate.] The army of the Union was drawn up to oppose the Spaniards. But there was no harmony amongst the leaders; no spirit in the troops. Falling upon one town after another, Spinola now brought into his power nearly the whole of that portion of the Palatinate which lay on the left bank of the Rhine. The army of the Union retreated helplessly to Worms, waiting for what might happen next. [Sidenote: § 10. Invasion of Bohemia.] Maximilian was now ready to attack Bohemia. He soon effected a junction with Bucquoi. Frederick's position was deplorable. [Sidenote: § 11. Growing unpopularity of Frederick.]