The challenge was accepted, war was declared, and Hannibal accomplished the amazing feat of leading an army of 60,000 men from Spain and effecting the passage of the Alps, while the Romans were landing an army in Spain.  In a brilliant campaign, he defeated the stubborn Roman legions at Vercellae and the Trebia.

But success depended not on the winning of victories by an isolated force, but on the disruption of Italy.  His superiority in the field was again demonstrated at Trasimenus, but no Italian allies came in.  He outwitted Fabius, and then utterly shattered at Cannae a Roman force of double his own numbers.  For a moment it seemed that Italian cohesion was weakening; but the Roman Senate and people were stirred only to a more dogged resolution.

Cannae failed to break up the Roman confederation.  Generalship unaided could accomplish no more.  In Spain, where young Scipio was soon winning renown, the Roman arms were in the ascendant, and in Sicily.  No effective aid was coming from Macedon, though war was declared between her and Rome.  Hannibal’s activities began to be paralysed; by slow degrees he was forced into the south.  Hannibal succeeded in crossing the Alps with fresh forces, but by a brilliant operation was annihilated on the Metaurus.  The time had come when Scipio could disregard Hannibal and strike at Carthage herself.  Even Hannibal’s return could not save her.  The victory of Zama decided the issue.  Carthage became virtually a tributary and subject state.  Spain was a Roman province, and North Africa a sort of protectorate.

The threatening extension of Macedonian power now demanded the protecting intervention of Rome; an honest act of liberation for the Greeks, but entailing presently the war with Antiochus of Syria.  Antiochus had left Phillip and Macedon in the lurch; now he sought to impose his own yoke in place of theirs.  The practical outcome was his decisive overthrow at the battle of Magnesia, and the cession to Rome of Asia Minor.  Pergamus, under the house of Actalus, was established as a protected kingdom, as Numidia under Masinissa had been.  The Greek states, however, were becoming conscious that their freedom was hardly more than a name; Perseus of Macedon once more challenged Rome, not without Greek support.  Macedon was finally crushed by Aemilius Paullus at Pydna.  From that moment, Rome dropped the policy of maintaining free states beyond the seas, which had manifestly failed.  Virtually, the known world was divided into subjects and dependencies of Rome, so vast was the change in the forty years between the battles of the Metaurus and Pydna.

Rapid extension of dominion by conquest had demoralising results; the ruling race was exposed to strong temptations in the provinces, and the city remained the seat of government, while the best of the burgesses were distributed elsewhere.  Hence, the popular assembly became virtually the city mob, while the ruling families tended more and more to form a close and greedy and plutocratic oligarchy.  The demoralisation was very inadequately checked by the austerity of the censorship as exercised by Cato.