The study of conflict is a search for certain truths and scientific rules to follow. This arises from the human desire for certainty, especially in human conflict---the most complex and perilous of endeavors. And there have been no shortage of thinkers offering iron, immutable rules of war. Antoine-Henri Jomini was perhaps the most influential of these theorists. A Swiss soldier serving in the army of Napoleon the first, he is probably the most influential military theorist of the 19th century.
Jomini's theories can be reduced to a simple set of instructions:
"That strategy is the key to warfare; that all strategy is controlled by invariable scientific principles; and that these principles perscribe offensive action to mass forces against weaker enemy forces at some decisive point if strategy is to lead to victory."
As John Shy notes in his review of Jomini in Makers of Modern Strategy, Jomini's strategy is a direct rejection of the limited-war strategies of monarchial war. If in doubt, attack!--the enemy must be pursued, scourged, and destroyed. What are the decisive points that must be attacked? Jomini is vague on this--he defines it as physical places that if lost, will "dislocate and ruin" the enemy. Victory comes from massing forces and throwing them into a fraction of the enemy's defense. Jomini identifies these operational principles with strategy in itself. He also proscribes operating in "interior lines"--concentrating all forces in attacks against one enemy than the next. These were Jomini's scientific truths of warfare.
In his time, Jomini had a much greater impact on doctrine than Clausewitz---the American Civil War strategies employed by both sides during the conflict were heavily influenced by Jominian theory. Alfred Thayer Mahan uses Jomini's concept of land warfare to build his conception of naval strategy. And modern operational art owes much to Jomini's tactical and operational thinking. Jomini, a practical-minded soldier from a (then) victorious French empire, offered more proscriptive insights than Clausewitz, a philosophical and abstract soldier from the then-defeated Prussian forces. It is not just a contrast in strategic views (certainly great as Clausewitz doubted the effectiveness of any fixed theory of warfare), but also in philosophical outlook.
You might even say that Jomini was an evangelist of sorts. There are lots of business, science, and world affairs books on the market that promise to reduce complicated real world phenomena to simplistic yet all-encompassing theories. They are written in catchy language and marketed with graphics. The New York Times' Thomas Friedman, who regales his readers with world-shattering revelations revealed to airport taxi drivers, is the master of this shallow genre. Although turgid and didactic by our standards, Jomini's The Art of War is a much more readable and catchy book than the massive and confusing On War.
Evangelists have their place--simplistic yet ambitious theories advocated by showmen can bring us to greater truths than objective but often useless theories, but only if we take them with a giant grain of salt. But the danger in Jomini's approach comes from its reductiveness. Tactical and operational methods are dependent on ever-shifting technological and social conditions, and Jomini's insistence on the massing of forces did not age well. The great slaughter of the Civil War, Russo-Japanese War, and first World War revealed the peril of massing men into groupings that could be chewed up by quick-firing guns and fires in massed attacks. The German army's use of decentralized infiltration tactics--which Jomini would view as a cardinal sin against the "higher laws" of warfare--was a forced adaptation to the nature of this new battlefield. Jomini's own sin was to mistake the conditions of his time for the eternal principles of strategy.
Strangely, cyberspace may be the one operational environment where Jomini's principles may still apply. As Oxford academic Audrey Kurth Cronin writes, our era of is one of "cyber-mobilization," where states and sub-state movements harness the rage of their people into information militias massed in cyberspace. Cyber-operations by hacker militias depend on massing force (e.g. botnets executing distributed denial of service attacks) on decisive points--such as crucial websites or servers.
Swarming, a technique employed by substate militias waging netwar, also involves the pulsing of distributed elements into tactical human swarms reliant on crowd intelligence. Jomini, a man of the French revolution, saw his method of warfare as an advantage over the timid and useless limited wars of the monarchy. While he later became a reactionary suspicious of popular wars, he most likely would be very interested in the idea of cyber-militias and netwar, though he would abhor their nonlinear nature.
Jomini's influence also lives on in reductionist theories of war advanced by figures as diverse as "indirect approach" theorist Basil Liddell-Hart and Vietnam-era Secretary of Defense Robert McNamara. Systems thinking in particular, Milan Vego writes, promotes an unrealistic view of war as an operational game that is dangerously disconnected from the real world. Paret notes in his chapter on Jomini that his simple theories are at the heart of equally simplistic theories of airpower that hold that enemies can be defeated through expertly calculated attacks on nodal points. Systems thinking holds that one can compel X if Y, but human complex adaptive systems resist such reductionism.
When such thinking is applied to grand strategy--the mechanistic doctrine of neorealism in international relations is a good example--the result is something like the fallacy of the Cold War-era "domino theory," ignoring the human, psychological, and cultural elements that go into the complex mix of human behavior. Systems thinking has its place in its holistic organizing power, but any systemic explanation should be regarded as less an iron law than a distorted reflection of a truth we strive for.