War has been a fact of human life as long as history itself, and has often been its determining factor. But what makes a military encounter "decisive?” For military historian John Colvin, it is when the outcome can be measured on a scale far wider than simple victory or defeat, when it can be seen to affect immediate history. Here, he discusses more than 20 battles that are recognizable turning points, from Salamis in 480 BC, through Hastings and Yorktown, to some of the major conflicts of the 20th century. Written with elegance and expertise, this is a work that illuminates a complex area of history.