One vision. One Purpose. Peace through Power.
-- Motto, the Brotherhood of Nod
Sometimes in fiction we see terrorist groups and various anti state groups capable of go toe to toe with regular army of the state. They may have the capacity to field aircraft, tanks, even battleships... almost as if they had billions in tax revenue and massive installed infrastructure themselves. Particulary eregrous are examples where these groups are shown fighting battles against modern Great Powers like USA, Russia, the EU, China, India, ect.
Needless to say this is highly unrealistic. A modern Main Battle Tank costs $100 a pop, a battleship can cost a billion dollors. Al Qaeda contested Iraq with barely 500 fighters, the Viet Cong had AP Cs
and the occasional Light Tank, but they had the might of the USSR supporting them. The Taliban were defeated by a cavalry charge
. The only rebel movement to ever have an airforce, the LTTE, could field a proud armada of 5 swedish trainer propeller planes. Although this doesn't mean that such irregular forces can not win, but to do that they need the tactics to match their strengths, namely Guerilla Warfare.