In 1672, however, Holland being threatened by Louis XIV., he concluded a treaty with the republic, engaging to furnish 20,000 men for its defence. He also contributed to induce the emperor: Denmark, Hesse Cassel, and several German princes to join him against France. But though his advance into Westphalia induced the French to quit Holland, the campaign was rendered unsuccessful by the slowness of the Austrian general, and he was forced to abandon Westphalia to the enemy. The Austrians leaving him, and the Dutch neglecting to send him subsidies, he was obliged to make a convention with France in 1673. The French were to evacuate Westphalia and pay him 800,000 livres, he promising to withdraw from his alliance with Holland, and not to support the enemies of France; yet he reserved to himself the right of assisting the German emperor in case of attack. This happened in 1674, when he invaded Alsace with 16,000 men, and joined the Imperial army; but the Austrian general, Bournonville, avoided a battle, contrary to the advice of Frederick, and Turenne receiving reinforcements obliged the Germans to quit Alsace. In order to free themselves from Frederick, the French instigated the Swedes to invade Pomerania and Altmark, which they attacked in December, 1674, with 16,000 men. Frederick hastened to his dominions, and proceeding with great rapidity and secrecy at the head of only 5,000 men, he totally defeated 11,000 Swedes at Fehrbellin in 1675, and freed his dominions from the enemy. Following up his successes, he took Stettin. In January, 1679, he crossed the Frische Haff and the Gulf of Courland with his army on sledges over the ice, and surprising the Swedes in their winter quarters, compelled them to quit Prussia. He did not reap any real advantage from his success, for Louis XIV. insisted that he should make peace with Sweden and give up all his conquests; and on his refusal, sent an army of 30,000 men to lay waste the duchy of Cleves, and city of Minden, so that he was forced to conclude the treaty of St. Germain, by which he restored all his conquests to Sweden; the French withdrew from his Westphalian dominions, and paid him 300,000 crowns.