Original sentence: Perhaps for these reasons, Yan chose to move its capital to Ji, which remained known as Jicheng or the City of Ji.The State of Yan would continue to expand until itbecame one of the seven major powers during the Warring States Period (473-221 BC)
Edited sentence: Perhaps for these reasons, Yan chose to move its capital to Ji, which remain to be known as Jicheng or the City of Ji.The State of Yan would continue to expand until it became one of the seven major powers during the Warring States Period (473-221 BC)