[Sidenote: Austrian intervention invoked] [Sidenote: Attitude of France] Austria, whose own dominions in Italy were threatened, had every reason to grant this request. The only obstacle was the threatening attitude of France. Before sending out his troops, Metternich took pains to ascertain the immediate intentions of France. The official answer given to the inquiries of the Austrian Ambassador in Paris, was that Austrian intervention in favor of the sovereigns of Parma and Modena, who were related to the House of Hapsburg, might be tolerated. An extension of such intervention to the Papal States or to Piedmont would certainly constitute a _casus belli_. In token of this declaration, the French Ambassador at Constantinople was instructed to make overtures for an offensive and defensive alliance to the Sultan. [Sidenote: Metternich diplomacy] [Sidenote: Papal dominions invaded] [Sidenote: Casimir Perier's French policy] In this crisis Metternich put forth all the powers of statesmanship at his command. He declared that it was better for Austria, if necessary, to perish by war than by revolution. On the instant he assured to Russia the support of Austria against the Poles, while he worked upon the fears of Louis Philippe by pointing to the presence of young Louis Bonaparte and his brother with the Italian insurgents. As a last resort he could always let loose upon France Napoleon's son, the Duke of Reichstadt, now growing to manhood at Vienna. In defiance of the French declaration, Austria advanced a strong army through northern Italy into the papal dominion. The insurrection was ruthlessly stamped out. Louis Philippe did nothing. Lafayette resigned his Ministry in chagrin. He was succeeded by Casimir Perier, a constitutional statesman of modern mold. On behalf of France he put forward a double-edged demand that the Austrians should evacuate the papal dominions as soon as the papal government should reform its abuses. For the first time in their history, Austria and the Papacy were made to declare for constitutional reforms. A conference at Rome agreed upon the schemes of reforms to be instituted by the Pope. Further pretext for revolution was thus removed. In July, the last Austrian forces were withdrawn from the Papal States. [Sidenote: War in Poland] [Sidenote: Early successes] [Sidenote: Polish disasters] [Sidenote: Ostrolenka] [Sidenote: Ravages of cholera] [Sidenote: Death of Diebitsch] [Sidenote: Civil war in Poland] [Sidenote: Paskievitch, Russian commander] [Sidenote: Fall of Warsaw]