Answer:
Hannibal Barca was defeated by
1.division of his army during expedition(his army was united of many warriors from different nations)
2.All of his soldiers got tired after 15 years of expedition which was taken in Europe. Therefore, he couldn't fight.
3. Roman Gerneral, Scipio knew Hannibal's tatics.
4.When Hannibal came back from Rome, his soldiers did not even have had a single fight for 15 years.(loss of train).