 Complete the following phrase:  It was, therefore, as a Prussian diplomat that Bernstorff attended the Congress of Aix-la-Chapelle October 1818, at the close of which he returned to Berlin as minister of state and head of the department for foreign affairs. Bernstorffs management of Prussian policy throughout the many years that he remained in office has been variously judged. He was by training and temperament against the Revolution, and he was initiated into his new duties as a Prussian minister by the reactionary Ancillon. He is accused of having subordinated the particular interests of Prussia to the European policy of Metternich and the Holy Alliance. Whether any other policy would in the long run have served Prussia better is a matter for speculation. It is true that Bernstorff backed the Carlsbad Decrees, and the Vienna Final Act; he was also the faithful henchman of Metternich at the congresses of Laibach, Troppau and Verona. On the other hand, he took a considerable share in laying the groundwork of the customs union Zollverein, which was destined to be the foundation of the Prussian hegemony in Germany. In his support of Russias action against Turkey in 1828 also he showed that he was no blind follower of Metternichs views. In the crisis of 1830 his moderation in face of the warlike clamour of the military party at Berlin did much to prevent the troubles in Belgium and 