Though nominally an ally in the coalition, Russia remained a dormant entity for much of the year (giving virtually no military aid to Prussia in the main battles that October, as Russian armies were still mobilising). Russian forces would not fully come into play in the war until late 1806 when Napoleon entered Poland. Finally, Prussia had remained at peace with France the previous year, though it did come close to joining the Allies in the Third Coalition. A French corps led by Marshal Bernadotte had illegally violated the neutrality of Ansbach in Prussian territory on their march to face the Austrians and Russians. Anger by Prussia at this trespass was quickly tempered by the results of Austerlitz, and a convention of continued peace with France was signed two weeks after that battle at Schönbrunn. This convention was modified in a formal treaty two months later, with one clause in effect promising to give Hanover to Prussia in exchange for Ansbach's being awarded to France's ally Bavaria. In addition, on 15 March 1806 Napoleon elevated his brother-in-law Marshal Joachim Murat to become ruler of the Grand Duchy of Berg and Cleves (acquired from Bavaria in return for its receiving Ansbach). Murat exacerbated Prussian enmity by tactlessly ejecting a Prussian garrison that was stationed in his newly acquired realm, prompting a stern rebuke from Napoleon. Relations between France and Prussia quickly soured when Prussia eventually discovered that Napoleon had secretly promised to return sovereignty of Hanover back to Britain during his abortive peace negotiations with the British. This duplicity by the French would be one of the main causes for Prussia declaring war that autumn. Another cause was Napoleon's formation in July 1806 of the Confederation of the Rhine out of the various German states which constituted the Rhineland and other parts of western Germany. A virtual satellite of the French Empire with Napoleon as its "Protector", the Confederation was intended to act as a buffer state from any future aggressions from Austria, Russia or Prussia against France (a policy that was an heir of the French revolutionary doctrine of maintaining France's "natural frontiers"). The formation of the Confederation was the final nail in the coffin of the moribund Holy Roman Empire and subsequently its last Habsburg emperor, Francis II, changed his title to simply Francis I, Emperor of Austria. Napoleon consolidated the various smaller states of the former Holy Roman