The tale of Ramayana is based on a historical event of crucial importance in far back times when humanity was at one of the critical crossroads of evolution. There was the lineage of solar dynasty kings who were born to lead humanity towards high and noble values. But alongside with them there were two more distinct shades of the human type that had also grown in power and strength. The land of the event was Aryabhoomi where the lineage of Ikshavaku and Raghu ruled with the highest Aryan ideals on the northern side of the Gangetic planes. The mid region was occupied by forest dwellers who were physically strong and mighty, closer to the animal in physique and who wore animal skin as a disguise and a way of life, like the Vanaras and the Riksha (bear). Down south was the Asura kingdom of Ravana who was slowly expanding it northwards with the help of the Rakshasas of Dandakaranya and his lieutenants like Marich, Subahu, Tadaka etc.
Though it was a part of their design, they did not or could not penetrate the impregnable Ayodhya. Sooner or later the conflict had to happen given the growing power and menace of Ravana trying to occupy territory and destroy the hermitages of Rishis and the Aryan culture. It is in the course of testing the Vanaras, to see whether he can overpower them that he had tried to challenge Bali but only to be humiliated. Since then, Ravana had made a pact of friendship with Bali which could have been potentially a deadly alliance for the civilisational values nurtured by the noble Aryans.
Now Bali, king of the Vanara kingdom. He seemed to be moving along the lines of a brute beast where might is right as is reflected through some of his stories and dealings with his brother. Yet, as arranged in the divine dispensation of things, Sugriva and Hanuman are part of the Vanara kingdom almost challenging Bali’s ways of life. In other words, the evolution of Vanaras was at juncture wherein they could either go the Asuric way through Bali and Ravana or else go the nobler humane ways through Hanuman and Sugriva. By removing Bali, Rama secured not only Kiskindha from becoming a menace or a vassal state of Ravana and his type but also secured a better and higher evolutionary possibility for the Vanaras.
This is the gist. The rest of it is incidental which I have already explained in a talk “श्री अरविंद और मानव भविष्य | TH 499”. Bali had to go for India to be secured against the Asura and to keep the flame of dharma growing in Aryavarta. The friendship with Sugriva, the method of killing Bali whom one could not defeat in frontal combat due to his capacity to draw half the opponents’ strength into himself, yet giving him an equal match by shooting through the seven palm trees as a sign that strength for strength Bali was still no match for Lord Rama are simply the outer conditions of the Divine Play.
The core was that Bali had to be eliminated for establishing the reign of dharma in Aryavarta.
