Analysts Molly K. McKew and Gregory A. Maniatis for WaPo:

Putin is no longer bound by the constraints of nation-state warfare. Years of confrontations with separatists, militants, terrorists and stateless actors influenced his thinking. In Crimea, Putin debuted a pop-up war — nimble and covert — that is likely to be the design of the future.

First, the hidden army appeared out of nowhere. Soldiers-of-no-nation were outfitted for troublemaking and street-fighting. These troops, denied by Putin, are also seemingly unconstrained by the laws, rules and conventions governing warfare — Putin’s biggest brush-off yet to international order. They are Putin’s hybrid of soldiers and terrorists: hidden faces, hidden command-and-control, hidden orders, but undoubtedly activated to achieve state objectives. The lack of an identified leader gums up the international community’s response: There is no general with whom to negotiate a cease-fire or surrender; if violence erupts, there is potentially no way to end it short of stopping each gunman.

These irregular forces are also a psychological menace for the local population and Ukrainians nationwide, who don’t know where else the hidden army awaits.

The second component of Putin’s 21st-century warfare is cyber. Calling it propaganda diminishes the insidious and poisonous nature of this information battle.

Two decades ago or more, James Dunnigan and Austin Bay wrote about our future of fighting “little wars” against non-traditional (and possibly non-state) actors. They couldn’t have been more correct in their assessments.

What Putin has done is quite remarkable. He’s taken the little war concepts traditionally used by small nations, rebels, or terror groups, and adapted them for use by a large nation-state.

These tactics act as a force multiplier, especially since the cyber actions and the semi-demi-guerrilla army require less force — and less logistical strain — than a conventional war does. Added to the mix what the authors describe as Putin’s talent for “using financial markets as a polemical tool” to keep himself enriched and in power.

Combatting this multi-layered and asymmetrical warfare, scaled up to continental size, is going to require a much more nimble White House, State Department, and Pentagon than we currently enjoy.