A French army under Guillaume Brune crossed the Swedish border on 13 July with 40,000–50,000 men and, after two days of hopeless Swedish resistance, initiated a Siege of Stralsund. Stralsund was captured on 20 August, as the Swedes transferred their forces to the island of Rügen. On 25 August the Swedish island of Dänholm was captured, after which the Swedish troops were allowed free departure to Sweden proper—thus having left all of Swedish Pomerania in French hands by 7 September. Sweden was ultimately forced to surrender on 6 January 1810 and enter the Continental System, after having suffered a Russian invasion from the east, as well as a Danish attack from the west.