Scott L. Wheeler, "Terrorist Tactics for War With the West," Insight on the News, January 6, 2003
Edit M. Lederer, "U.S. Special Forces In Increasing Demand All Over The World," Associated Press Worldstream, November 1, 1994
Second generation warfare was a response to the rifled musket, breechloaders, barbed wire, the machinegun, and indirect fire. Tactics were based on fire and movement, and they remained essentially linear. The defense still attempted to prevent all penetrations, and in the attack a laterally dispersed line advanced by rushes in small groups. Perhaps the principal change from first generation tactics was heavy reliance on indirect fire; second generation tactics were summed up in the French maxim, "the artillery conquers, the infantry occupies." Massed firepower replaced massed manpower. Second generation tactics remained the basis of U.S. doctrine until the 1980s, and they are still practiced by most American units in the field.
While ideas played a role in the development of second generation tactics (particularly the idea of lateral dispersion), technology was the principal driver of change. Technology manifested itself both qualitatively, in such things as heavier artillery and bombing aircraft, and quantitatively, in the ability of an industrialized economy to fight a battle of materiel (Materialschlacht).
The second generation saw the formal recognition and adoption of the operational art, initially by the Prussian army. Again, both ideas and technology drove the change. The ideas sprang largely from Prussian studies of Napoleon's campaigns. Technological factors included von Moltke's realization that modern tactical firepower mandated battles of encirclement and the desire to exploit the capabilities of the railway and the telegraph.
Third generation warfare was also a response to the increase in battlefield firepower. However, the driving force was primarily ideas. Aware they could not prevail in a contest of materiel because of their weaker industrial base in World War I, the Germans developed radically new tactics. Based on maneuver rather than attrition, third generation tactics were the first truly nonlinear tactics. The attack relied on infiltration to bypass and collapse the enemy's combat forces rather than seeking to close with and destroy them. The defense was in depth and often invited penetration, which set the enemy up for a counterattack.
While the basic concepts of third generation tactics were in place by the end of 1918, the addition of a new technological element-tanks-brought about a major shift at the operational level in World War II. That shift was blitzkrieg. In the blitzkrieg, the basis of the operational art shifted from place (as in Liddell-Hart's indirect approach) to time...
In broad terms, fourth generation warfare seems likely to be widely dispersed and largely undefined; the distinction between war and peace will be blurred to the vanishing point. It will be nonlinear, possibly to the point of having no definable battlefields or fronts. The distinction between "civilian" and "military" may disappear. Actions will occur concurrently throughout all participants' depth, including their society as a cultural, not just a physical, entity. Major military facilities, such as airfields, fixed communications sites, and large headquarters will become rarities because of their vulnerability; the same may be true of civilian equivalents, such as seats of government, power plants, and industrial sites (including knowledge as well as manufacturing industries). Success will depend heavily on effectiveness in joint operations as lines between responsibility and mission become very blurred. Again, all these elements are present in third generation warfare; fourth generation will merely accentuate them.
William S. Lind et al., "The Changing Face of War: Into the Fourth Generation," Military Gazette, October 1989