When Napoleon Bonaparte started to expand eastwards in the Napoleonic Wars, the Swedish Empire initially maintained a neutral stance. In 1805, Gustav IV Adolf of Sweden entered the War of the Third Coalition on the anti-French side, primarily to strip Napoleon's ally Denmark of Norway. His Norwegian ambitions were thwarted by several military and diplomatic setbacks
Stralsund, a port in Swedish Pomerania, was defended by the Swedish governor Hans von Essen. On 28 January, French forces commanded by Marshal Mortier crossed the Peene River in an attempt to impose a blockade on Stralsund. To the east, General of Division Jean Sebastien Grandjean's division crossed the Peene at Anklam, driving back the Swedish outposts. To the west, General of Division Pierre Louis Dupas' division crossed the stream unopposed near Demmin. On the 29th, Mortier's two divisions appeared before the port and on 30 January began the blockade.
Édouard Mortier (left) and Gustav IV Adolf of Sweden (right)For the next two months, the two sides fought a number of skirmishes as the French strengthened their lines of investment. Without control of the island of Rügen, the French were unable to interrupt Stralsund's sea communications and were harassed by Swedish gunboats. During the blockade, one French cavalry and three infantry regiments were taken from Mortier to fight against the Russians in Poland and replaced by troops from the Kingdom of Holland.
On 29 March, Mortier received orders to leave Grandjean's division to maintain the blockade and march to assist in the Siege of Kolberg in Brandenburg-Prussian Pomerania. After Mortier left, Essen drove Grandjean's outnumbered troops from their lines. Grandjean fell back to Anklam where he was attacked again on 3 April and forced to retreat southeast to the fortress of Stettin on the Oder, arriving there on the 7th. Mortier retraced his steps and by 13 April had assembled 12,000 to 13,000 men at Stettin, about the same number as Essen. In very wet weather, Mortier began pressing Essen back to Anklam. On 16 April, Mortier defeated the Swedes in the Battle of Belling. The next day, Essen retreated to the north bank of the Peene.
Beginning on 18 April, the French and Swedish forces arranged the truce of Schlatkow. Anxious to employ Mortier's men against the Russians and Prussians, Napoleon had authorized the marshal to make a truce with the Swedes. For their part, the Swedes were upset that England had given them very little support. By the 29th, the terms were worked out. The Swedes were to stay on the north side of the Peene. They handed over the islands of Usedom and Wolin at the mouth of the Oder and promised not to help the Prussians at the sieges of Kolberg (Kolobrzeg) or Danzig.