Complex sentence: The concept of Three Kingdoms which consist of (Goguryeo, Silla, and Baekje) was given by Korean people.Silla, and Baekje dominated the peninsula and Goguryeo control parts of Manchuria of China and part of Korean peninsula at beginning of the 1st century AD.
Split into simpler sentences: The concept of Three Kingdoms which consist of (Goguryeo, Silla, and Baekje) was given by Korean people. Silla and Baekje dominated the peninsula while Goguryeo controlled parts of Manchuria and part of the Korean peninsula at the beginning of the 1st century AD.