There are two key words to keep in mind when reading Thomas Ricks’s important and eminently readable new book, “The Generals”: accountability and relief. Accountability is what set Ricks out on his investigation of America’s military leaders from World War II to the present, as in the missing accountability of our generals for the failures of the post-9/11 decade of conflict in Iraq and Afghanistan. And relief is what Ricks believes has been too often missing, as in the old-fashioned sense of the word and one that is hardly ever used anymore, certainly by the U.S. military: firing.