We are only six weeks into Vladimir Putin’s war against Ukraine, but the conflict has already settled into a familiar pattern. Both sides often go into wars with a theory of victory, and it is only when both theories fail that the true shape of the conflict begins to appear. In the Second Punic War (218-201 B.C.), Hannibal thought that if he could get an army into Italy and win some conspicuous victories, the other Italian city-states, restless under Roman rule, would revolt and enable him to break Roman power for good. The Romans thought that their superior legions with their fighting spirit and discipline would quickly show Hannibal who was boss.

Both sides discovered that their initial strategies did not work. The Romans were shocked by a series of disastrous military defeats and faced the greatest challenge in Roman history. Hannibal achieved his initial goals, getting his army over the Alps and winning a series of dramatic victories, still studied today by ambitious young military officers all over the world. But his strategy failed. Even after his overwhelming victory at Cannae, only a handful of Italian city-states went over to his side. Roman power survived, and the war dragged on.

World War I started out in much the same way. The French and the Germans had both planned what they hoped would be decisive attacks, the French over their eastern border and the Germans with the Schlieffen plan for an attack through Belgium that would capture Paris. Both offensives fell short, leaving the countries locked in a conflict that neither side knew how to win—and neither was willing to lose.

Something similar seems to be happening with Mr. Putin’s war. The original Russian plan was to break the Ukrainian state by quickly taking the capital and major cities such as Kharkiv. It failed. Ukraine hoped that the shock of military setbacks plus major economic sanctions would either force Mr. Putin to accept peace terms favorable to Ukraine or lead to his overthrow. That plan also seems to have failed, at least for now.