How Did Hannibal Lose the Second Punic War When He Was a Military Genius.

When the Second Punic War began, the Romans did not have any generals who were remotely Hannibal’s equal in battlefield tactics. Hannibal demolished the Roman army at the Battles of Ticinus, Trebia, and Trasimene. Then the Romans elected Quintus Fabius Maximus dictator and he promoted a novel idea: Let’s not fight Hannibal on his terms but do everything we can to prevent him from feeding his army.
That was a very un-Roman idea, but it might well have worked in another year or two. Unfortunately, the idea was not popular among the Romans, and they elected as Consul Gaius Terentius Varro who swore to destroy Hannibal and his army on the first day he made contact with them. The subsequent Battle of Cannae was an absolute disaster for the Romans with some 55,000 Roman and allied soldiers dead and about 10,000 others captured and sold into slavery.
After the debacle at Cannae, Fabius was once again in charge and Rome largely avoided set piece battles with Hannibal. Unfortunately, many tribes and cities of Italy went over to Hannibal after the Battle of Cannae, thinking they were joining the winning side.
The war became one of attrition which Hannibal could not win. The Romans concentrated upon retaking the territories that went over to Hannibal after Cannae. They successfully besieged Capua and took Tarentum by a ruse, selling the populations of both cities into slavery. By 206 B.C. they had Hannibal bottled up in a small territory in Bruttium. It did not help that the Carthaginians did not send him a lot of supplies or reinforcements. There were plans to do so in 215 B.C. but Hannibal’s brother Hasdrubal lost a major battle at Dertosa in Spain, and the Carthaginians, fearing to lose their wealthy province in Spain, sent two armies of 25,000 each to Spain and sent Hannibal only 4000 Numidian mercenaries and 20 elephants. This would be the last assistance Hannibal would receive from Carthage, either because the Carthaginians didn’t authorize any or because the increasingly vigilant Romans prevented its delivery.
Both of Hannibal’s brothers, Hasdrubal and Mago, brought armies to Italy in an attempt to reinforce Hannibal. Hasdrubal and his army were destroyed at the Battle of the Metaurus River in 207 B.C., and Mago, although he established a beachhead in Liguria, was never able to unite with Hannibal as the Romans kept a close guard on the passes to the south.
This war of attrition would have ended in a stalemate except for the accomplishments of one Roman: Publius Cornelius Scipio Africanus. Scipio went to Spain to take command of the legions there after his father and uncle were killed at the Battle of the Baetis River. Within four years he had captured the Carthaginian port of New Carthage, defeated the Carthaginians at the Battles of Baecula and Ilipa and drove all of the Carthaginian military out of Spain. Then he returned to Rome, got elected to Consul and planned an invasion of Africa. After he wreaked havoc in Africa, the Carthaginians called Hannibal home and he and Scipio confronted each other at the Battle of Zama. It was a decisive victory for the Romans and Carthage was forced into a treaty on Roman terms.