In plain words
When he also took into himself the two kalās of Paraśurāma, Rāma shone forth complete in all sixteen kalās.
After some time Daśaratha, realising that old age had come upon him, resolved to crown as king Śrī Rāma, the son of the chief queen. The whole kingdom rejoiced. Everyone felt that Rāma alone was fit to rule the kingdom. Hearing this news, Mantharā went to Kaikā: “Mother, Daśaratha has forgotten the word he gave your father when he married you. By right it is your son who should be crowned,” she said. Not only that: she also reminded her that Daśaratha had given her two boons for helping him in the war of the gods and the demons, and said that this was the right time to ask for them. In truth Kaikeyī loved Rāma more than her own son Bharata. But her mind was poisoned by Mantharā’s evil counsel; at once she took off all her jewels, threw them away and went into the chamber of anger.
Śrī Rāma keeps his father’s word
When Daśaratha went to Kaikā to tell her first the news of Śrī Rāma’s coronation, he learnt that she had gone into the chamber of anger and was dismayed. He found out the reason and gave his word that he would grant the two boons she asked. Then Kaikā voiced her first wish: that her son Bharata be crowned. Her second wish, however, was a very harsh one. “For fourteen years Rāma must be sent to the forest,” she said. At those cruel, harsh words Daśaratha was shattered. “I will surely crown your son. But give up the thought that Rāma must live in the forest”: so he tried hard to persuade her. But Kaikā did not give up her insistence. Learning of this, Rāma took keeping his father’s word to be his duty and at once made ready to leave for the forest.