Complex sentence: From the 1910s until his death, Van Loon wrote many books, most notably "The Story of Mankind", by far his most well-known book, a history of the world especially for children which won the first Newbery Medal in 1922.
Split into simpler sentences: From the 1910s until his death, Van Loon wrote many books. Most widely known among these is "The Story of Mankind", a history of the world especially for children, which won the first Newbery Medal in 1922.