A further incident contributed not a little to increase the firmness of the Protestant princes. The King of Sweden had, at last, overcome the scruples which had deterred him from a closer alliance with France, and, on the 13th January 1631, concluded a formal treaty with this crown. After a serious dispute respecting the treatment of the Roman Catholic princes of the empire, whom France took under her protection, and against whom Gustavus claimed the right of retaliation, and after some less important differences with regard to the title of majesty, which the pride of France was loth to concede to the King of Sweden, Richelieu yielded the second, and Gustavus Adolphus the first point, and the treaty was signed at Beerwald in Neumark. The contracting parties mutually covenanted to defend each other with a military force, to protect their common friends, to restore to their dominions the deposed princes of the empire, and to replace every thing, both on the frontier and in the interior of Germany, on the same footing on which it stood before the commencement of the war. For this end, Sweden engaged to maintain an army of 30,000 men in Germany, and France agreed to furnish the Swedes with an annual subsidy of 400,000 dollars. If the arms of Gustavus were successful, he was to respect the Roman Catholic religion and the constitution of the empire in all the conquered places, and to make no attempt against either. All Estates and princes whether Protestant or Roman Catholic, either in Germany or in other countries, were to be invited to become parties to the treaty; neither France nor Sweden was to conclude a separate peace without the knowledge and consent of the other; and the treaty itself was to continue in force for five years. Great as was the struggle to the King of Sweden to receive subsidies from France, and sacrifice his independence in the conduct of the war, this alliance with France decided his cause in Germany. Protected, as he now was, by the greatest power in Europe, the German states began to feel confidence in his undertaking, for the issue of which they had hitherto good reason to tremble. He became truly formidable to the Emperor. The Roman Catholic princes too, who, though they were anxious to humble Austria, had witnessed his progress with distrust, were less alarmed now that an alliance with a Roman Catholic power ensured his respect for their religion. And thus, while Gustavus Adolphus protected the Protestant religion and the liberties of Germany against the aggression of Ferdinand, France secured those liberties, and the Roman Catholic religion, against Gustavus himself, if the intoxication of success should hurry him beyond the bounds of moderation.