All ideas are from William S. Lind in his article: "The Four Generations of Modern Warfare"
From Lind's article he describes the evolution of warfare dating from the Peace of Westphalia in 1648 to the present in four categories:
The 1st Generation of War (from 1648-present): Lind describes this generation of warfare involving the state having control over all military affairs. In addition, the emphasis on order was imbedded in military culture and battles above all else. It was not until the American Civil War that the the battlefield would become less orderly and decentralized. In turn, this meant the ending of the domination of 1st Generation of war tactics and culture and an inter-period before the new generations would implant themselves.
The 2nd Generation of War (from WW1-present): Lind describes this generation of war developed by the French as one of proposed solutions of handling the contradiction of having a orderly military culture and a disorderly battlefield. This kind of warfare focused on "firepower/attrition warfare", the military being a hierarchy, and had the military officers impose obedience on their soldiers. In essence, it could be said that the Second Generation of War was an updated version of the first.
The 3rd Generation of War (from WW1-present): Lind describes this generation of war developed by the Germans as the second of the proposed solutions of handling the contradiction. This generation focused on maneuverability rather than firepower. In addition, it didn't want a hierarchy in military culture and focused on emphasizing that the soldier could discipline themselves and adapt themselves to the battlefield contrary to what their superiors ordered in order to get results on the battlefield. This warfare strived to be clever in defeating their enemies rather than imposing their will with firepower like the French.
The 4th Generation of War (present day): Lind argues that the 4th Generation of War parallels the pre-1st Generation of War tactics. Terrorism is not an orderly force controlled by a state but a decentralized and disperse entity that focuses on fighting for a culture or religion. Lind also implies that the previous generations of war and their tactics won't work against this stateless entity.
All generations of warfare are practiced today in some way.
So what is going to be the 5th generation of warfare?