Risk is a modern designed game with no historical chess-family lineage, so it sits apart from Chess and its relatives.
Modern Conquest and War Games covers 20th-century commercial games of territorial conquest or negotiation among players, such as Diplomacy, Risk and Stratego, that were designed without a traditional chess-family lineage. Chess and its historical relatives are grouped instead under Chess-Family War Games because they descend from or parallel the ancient game of Chaturanga.