When Ravana kidnapped Sita, Vibishana advised Ravana to return Sita, but he did not heed to his words. After this incident, Vibishana decided to join the side of Lord Rama. He instructed his daughter, Thrijata to look after Sita well. Only his wife and daughter knew that he joined the side of Lord Rama. Upon joining Lord Rama, he disclosed many key secrets which were crucial in the war of Ramayana for their victory.
In order to cross over from India to Lanka, Lord Rama decided to pray to the water god in order to ask him to keep the waters still, so that they could cross to Lanka across the ocean. So, Lord Rama meditated for an entire day, but after getting no response from the water god, he started to attack the fishes in the ocean. Immediately, the water god appeared and granted Lord Rama’s wish. Then he ordered the monkeys to build a bridge using the rocks. It took 5 days and 5 nights for the entire monkey army to build a rock bridge from India to Lanka. They did this with the help of stones that floated on water and after the bridge’s construction, Lord Rama and his army were able to cross over to Lanka.
Lord Rama came to Lanka and started attacking Ravana’s army with his troops. Ravana suffered major losses and decided to take the help of Kumbhakarna. Ravana then woke up his brother Kumbhakarna from sleep and told him about the situation. Kumbhakarna actually told Ravana to return Sita and stop this needless war. But, Ravana tricked Kumbhakarna into helping him by saying that he should help in the name of his forefathers. Now, Kumbhakarna was a pious person and hence could not turn down the request. So he went and fought with Lord Rama and his army. He was able to fight against Angad, Sugriva, Hanuman and also managed to kill a large number of Lord Rama’s army. Finally, after a big fight, Lord Rama managed to kill Kumbhakarna. As Kumbhakarna died, Ravana was ready to set foot on the battlefield.