It is one of the tragedies of recent cultural history that, thanks to Mel Gibson's preposterous movie "Braveheart," the world knows more about William Wallace's short-lived Scottish rebellion of 1296-97 than about Robert the Bruce. For it was Bruce who, after 18 years of plotting and war making, finally threw off the yoke of the English king and consolidated a sense of Scottish identity. "Never will we on any conditions be subjected to the lordship of the English," said the Declaration of Arbroath, a diplomatic letter commissioned by Bruce in 1320. "It is in truth not for glory, nor riches,...