Baekje was founded by Onjo, the third son of Goguryeo's founder Jumong and So Seo-no, at Wiryeseong (present-day southern Seoul). Baekje, like Goguryeo, claimed to succeed Buyeo, a state established in present-day Manchuria around the time of Gojoseon's fall.
Baekje alternately battled and allied with Goguryeo and Silla as the three kingdoms expanded control over the peninsula. At its peak in the 4th century, Baekje controlled most of the western Korean peninsula, as far north as Pyongyang, and may have even held territories in China, such as in Liaoxi, though this view is controversial. It became a significant regional sea power, with political and trade relations with China and Japan.
Baekje was a great maritime power; its nautical skill, which made it the Phoenicia of East Asia, was instrumental in the dissemination of Buddhism throughout East Asia and continental culture to Japan.
Baekje was founded in 18 BC by King Onjo, who led a group of people from Goguryeo south to the Han River basin. According to the Chinese Records of the Three Kingdoms, during the Samhan period, one of the chiefdoms of the Mahan confederacy was called Baekje.