Book excerpt: For over 2,500 years, the forbidding territory of Afghanistan has served as a vital crossroads for armies and has witnessed history-shaping clashes between civilizations: Greek, Arab, Mongol, and Tartar, and, in more recent times, British, Russian, and American. When U.S. troops entered Afghanistan in the weeks following September 11, 2001, they overthrew the Afghan Taliban regime and sent the terrorists it harbored on the run. But America's initial easy victory is in sharp contrast to the difficulties it faces today in confronting the Taliban resurgence. Originally published in 2002, Stephen Tanner's Afghanistan has now been completely updated to include the crucial turn of events since America first entered the country.