Guerrilla

Guerrilla is a term invented in Spain during the liberation war agains France. It means "little war".
It is based in small, mobile and flexible combat groups without a front line.

The U.S.A. learned in the Vietnam War that guerrilla tactics can be very effective. Vietcong would avoid battles with the Americans unless the odds were clearly in their favor. Instead they used hit and run attacks and ambushes.