Each generation of warfare builds on the last.
We can learn about first generation warfare through the collection of writings by Flavious Vegetius known as DeRe Militari. He was a roman citizen who in the late Roman Empire laid bare the mechanics of the roman legions. It has been the favorite of military commanders up until even the modern era for more then one reason. First generation battles were won and lost with columns and lines of men out maneuvering each other on a small scale field of battle. Combined arms were a key.
Second generation warfare can be found in the attrition of WWI. Trenches, artillery and machine guns lead to protracted battles. Combat was about everything supporting infantry and infantry taking and holding ground.
Third generation warfare came with the blitzkrieg of WWII. Speed of attack through mechanized troop movement made fixed line trench warfare a thing of the past. Infantry supported tanks, in theory.
Fourth generation warfare came with vertical envelopment. Mobile air infantry can take the battle to the enemy. Medical evacuation brought down casualty rates, although winning all the battles does not mean you win the war. Vertical envelopment is not conducive to holding ground.
Fifth generation warfare is psychological. From first generation warfare we learnt that all war is resource based. The most important resource in modern war is the human resource. Impressions generated from the media sources on TV and especially the internet can win and lose wars more then the situation on the ground can. Modern warfare is fought on with conventional troops, but also with private military contractors. Private military companies allow politicians to get certain results while maintaining a thin vale of plausible deniability. Executive outcomes I feel set the paradigm in motion. When private corporations began to supply a service that for many years was solely supplied by national governments or shadow governments people saw that more could be obtained with less. Less regulation and over site allow for nations to pay for a service on the front end without having to pay more on the back end, especially in terms of pensions and long term medical care. While the thin vale of plausible deniability is lifting and systems of accountability are coming into play there has yet to emerge a six generation of warfare.