Clashes between Chinese and Japanese forces at Pungdo and Seongwhan caused irreversible changes to Sino-Japanese relations and meant that a state of war now existed between the two countries. The two governments officially declared war on August 1. Initially, the general staff's objective was to secure the Korean peninsula before the arrival of winter and then land forces near Shanhaiguan. However, as the navy was unable to bring the Beiyang fleet into battle in mid-August, temporarily withdrew from the Yellow Sea to refit and replenish its ships. As a consequence, in late August the general staff ordered an advance overland to the Zhili plain via Korea in order to the capture bases on the Liaodong Peninsula to prevent Chinese forces from interfering with the drive on Beijing. The First Army with two divisions was activated on September 1. In mid-September 17, the Chinese forces defeated at Pyongyang and occupied the city, as the remaining Chinese troops retreated northward. The navy's stunning victory in the Yalu on September 17, was crucial to the Japanese as it allowed the Second Army with three divisions and one brigade to land unopposed on the Liaodong Peninsula about 100 miles north of Port Arthur which controlled the entry to the Bohai Gulf, in mid-October. While, the First Army pursued the remaining Chinese forces from Korea across the Yalu River, Second Army occupied the city of Dairen on November 8 and then seized the fortress and harbor at Port Arthur on November 25. Farther north, the First army's offensive stalled and was beset by supply problems and winter weather.