What is red flag?

Red flags can signify a warning, martial law, defiance, or left-wing politics. The earliest citation for "red flag" in the Oxford English Dictionary is from 1602 and shows that at that time the flag was used by military forces to indicate that they were preparing for battle.[1] It has been associated with left-wing politics since the French Revolution.[2] The red flag became a symbol of communism as a result of its use by the Paris Commune of 1871.[3] The flags of several communist states, including China, Vietnam, and the former Soviet Union, have red backgrounds. The Labour Party in Britain used it until the late 1980s, and the French Socialist Party uses it. The earliest citation of "red flag" in the sense of a warning is dated 1777 and refers to a flag warning of flood.[4] OR RED FLAG is an advanced aerial combat training exercise hosted at Nellis Air Force Base, Nevada and Eielson Air Force Base Alaska. Since 1975, air crew from the United States Air Force (USAF) and other U.S. military branches and allies take part in the exercises, each of which is six weeks in duration. The Red Flag exercises, conducted in four-to-six cycles a year by the 414th Combat Training Squadron of the 57th Wing, are very realistic aerial war games. The purpose is to train pilots from the U.S., NATO and other allied countries for real combat situations. This includes the use of "enemy" hardware and live ammunition for bombing exercises within the Nevada Test and Training Range