Editor's note: This will be Andrew Exum's final "Abu Muqawama" column at World Politics Review. We'd like to take this opportunity to thank Andrew for his engaging analysis and to wish him continued success in his many endeavors.
Green-on-blue violence -- attacks on U.S. and allied forces by their Afghan partners -- is the most serious tactical challenge to the NATO coalition since the war in Afghanistan began almost 11 years ago.
The name "green-on-blue" derives from U.S. military war games in which "blue" forces are friendly, "red" forces are enemy and "green" forces represent those of the host nation. ("Blue-on-blue" has thus long been the U.S. military shorthand for friendly fire incidents.)