Sword Demon Island is a Manga/Manhwa/Manhua in english language, HISTORICAL series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

When the war between the Justice Alliance and the Heavenly Demon Coalition, known as The Great Demon War, was at its peak, Sim Ho lived in the peaceful village of Baekriju. At the age of twelve, he becomes caught up in Jegal Hwi’s plot to take over Baekriju and is dragged to The Cheonil Plain, the war’s frontline. In the midst of a desperate battle, he encounters The Black Ox fighters, who save his life. He is then assigned to their group and thus begins the arduous journey to learn martial arts so that he can grow into a powerful warrior and return home to Baekriju…!