Maintain public order; prevent strife. For example, President Clinton ordered troops to Bosnia to keep the peace. This expression dates from the 1400s and was originally used more in the first sense, that is, of police keeping public order. It gained extra currency in the second half of the 1900s when military forces were sent to diverse places—Lebanon, Haiti, Bosnia—to stop warring factions.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.