 Although he rejoined the anti-French alliance in 1674, this left him diplomatically isolated; despite conquering much of Swedish Pomerania during the Scanian War, he was obliged to return these to Sweden in the 1679 Treaty of Saint-Germain-en-Laye.Frederick William was a military commander of wide renown, and his standing army would later become the model for the Prussian Army.He is notable for his joint victory with Swedish forces at the Battle of Warsaw, which, according to Hajo Holborn, marked "the beginning of Prussian military history", but the Swedes turned on him at the behest of King Louis XIV and invaded Brandenburg.