Walk off the reservation

Posted by Mr. HVHJ on June 18, 2007

To what does the word "reservation" in the phrase "walk off the reservation" refer? What is the origin of this phrase? I suspect it has something to do with Native American history, but I'm not sure.

Context (From "The Long View in Iraq" by Roger Cohen, NYTimes, June 17, 2007):

The last military build-up will not be repeated. Americans have no stomach for a further "surge" and the U.S. armed forces have no capacity for one. Republicans, facing an unpopular war, are going to walk off the reservation unless the president changes course in the fall.

• Walk off the reservation ESC 18/June/07