Board gamers with a thirst for world conquest have long been attracted to “Risk.” Its simple mechanics make it easy to learn, and the thrill of annexing nations through simulated force of arms appeals to a bellicose streak in all but the most devoted pacifists. Hasbro and Electronic Arts have done an excellent job making the tablet version as exciting as its board analog. The “board” for “Risk” for the iPad is a map of the world segmented into countries and regions. All territory is occupied by the armies of the players when the game begins.