Third-generation warfare focuses on using speed and surprise to bypass the enemy's lines and collapse their forces from the rear. Essentially, this was the end of linear warfare on a tactical level, with units seeking not simply to meet each other face to face but to outmaneuver each other to gain the greatest advantage.
The concept of fourth-generation warfare as presented by Lind et al. is characterized by a return to decentralized forms of warfare, blurring of the lines between war and politics, combatants and civilians due to nation states' loss of their near-monopoly on combat forces, returning to modes of conflict common in pre-modern times.
“Unmanned Systems Roadmap: 2007-2032”, Office of the Secretay of Defense (10 December 2007) — the report (12 meg PDF). “This roadmap provides Defense-wide vision for unmanned systems and related technologies. The Department will continue … updating it as transformational concepts emerge. Unmanned systems wil continue to have a central role in meeting our country’s diverse security needs, especially in the Global War on Terrorism.”