The unification of Germany after fierce struggles within and without naturally deflected historical scholarship from the path marked out by Ranke, who had grown to manhood in the era of political stagnation following the downfall of Napoleon. The master's Olympian serenity was deplored by the group of hot-blooded scholars who are collectively known as the Prussian School, and who were firmly convinced that the principal duty of historians was to supply guidance and encouragement to their fellow-countrymen in the national and international problems of the time. In his gigantic work on the History of Prussian Foreign Policy, Droysen, the eldest of the Triumvirate, calls four centuries to witness that the Hohenzollerns alone, from their unswerving fidelity to German interests as a whole, were fitted to restore the Empire. He worked exclusively from Prussian archives, and history seen exclusively through Prussian spectacles was bound to be one-sided. No student of European history would contest the value of his researches; but his interpretation of Prussian policy in terms of German nationalism was at once recognized as a fundamental error, and has long been abandoned. The second member of the group, Sybel, himself one of the three favourite pupils of Ranke, revolted in middle life, and in his two great treatises on the era of the French Revolution and the foundation of the German Empire championed the policy of the Hohenzollerns and delivered slashing attacks on France and Austria, their rivals and antagonists.