Watership Down

According to Adams' Lapine language, culture and mythology, the world was created by the god Frith, who represents the Sun. All animals lived harmoniously, but the rabbits eventually multiplied, and their appetite led to a food shortage. At the prayers of the desperate animals, Frith warned the rabbit prince El-ahrairah to control his people, but was scoffed at. In retaliation, Frith gave special gifts to every animal, but some animals he made predators to prey upon the rabbits. Satisfied that El-ahrairah (Now also known as "Prince with a Thousand Enemies") had learned his lesson, Frith also gave the rabbits speed and cunning; while many would seek to kill them, the rabbits could survive by their wits and quickness.
In the present, in the English countryside of Sandleford, Fiver, a rabbit seer has an apocalyptic vision and goes with his older brother Hazel to beg the chief to have the warren evacuated, but they are dismissed and attempt to make an exodus themselves. The group meets resistance from the warren's police force called the Owsla, but eight manage to fight and escape: Fiver, Hazel, Bigwig, Blackberry, Pipkin, Dandelion, Silver and Violet. As Fiver had foreseen, the warren is wiped out by human developers. The group travels through the dangerous woods and makes it to a bean field to rest. In the morning, Violet is killed by a hawk, leaving the group without a female.
After several dangerous situations, they meet the enigmatic rabbit Cowslip, who invites them to his warren. They are grateful, but Fiver senses something unsettling in the atmosphere, as well as the resident rabbits' overly resigned attitudes, and leaves. An irked Bigwig follows, and chastises Fiver for supposedly causing senseless tension with his instincts. Moments later, however, he is caught in a snare trap. Fiver attempts to get help from their hosts, but is ignored. Bigwig is freed after nearly dying. As Fiver reveals, the warren is fed by a farmer who snares rabbits in return for his food and protection from predators. After Bigwig's narrow escape, the other rabbits willingly follow Fiver's and Hazel's advice and set out once more.
The rabbits discover Nuthanger farm, which contains a hutch of female rabbits, necessary for a new warren. However, they do not manage to free them, on account of the territorial farm cat and dog. Later, they are found by the maimed Owsla Captain Holly, who recounts the destruction of Sandleford by humans, and a mysterious group called the "Efrafrans" before falling unconscious. After he recovers, Fiver finally leads the group to the hill he envisioned, Watership Down, where the rabbits settle in, with Hazel as chief.
They befriend an acerbic injured seagull, Kehaar, who offers to survey the local area for does. The rabbits return to Nuthanger Farm to free the does; Hazel is shot by a farmer and presumed dead, but Fiver has a vision and follows the apparition of the Black Rabbit of InlÃ© (a rabbit version of the Grim Reaper) to his injured brother. Kehaar returns and while removing buckshot pellets from Hazel's leg, reports of Efrafa, a large warren with many females. Holly, who encountered Efrafa, begs them not to go there, describing it as a totalitarian state, run by vicious and heavily territorial rabbits. Hazel feels they have no choice but to go there. Bigwig infiltrates the enemy warren and is made an Owsla officer by the cruel chief, General Woundwort. Bigwig recruits several potential escapees to his cause, including Hyzenthlay, an idealistic doe and Blackavar, a scarred attempted escapee. They flee, and using a boat to float down the river, they evade capture, helped by Kehaar. That night, Kehaar leaves for his homeland, with the gratitude of the warren.
Several days later, Efrafan trackers discover their trail and follow them to Watership Down. Hazel offers a treaty with Woundwort, who dismisses Hazel, telling him to turn over Bigwig and all the deserters or he will kill the entire warren. The Watership rabbits barricade their warren and are besieged by the Efrafans. Fiver slips into a trance, in which he envisions a dog loose in the woods. His moans inspire Hazel to free the dog from Nuthanger Farm and lead him to the Efrafans. He escapes with Blackberry, Dandelion and Hyzenthlay.
Hazel prays to Frith, offering his life for that of those in the warren, a bargain Frith acknowledges, but does not accept. Hazel releases the dog while his companions bait it into following them to Watership Down; Hazel is attacked by the cat, but saved by Lucy (the owner of the hutch rabbits). When the Efrafans break through the warren's defences, Woundwort goes in alone; Blackavar attacks him, but Woundwort slays him easily. Bigwig ambushes Woundwort and they fight to exhaustion. The dog arrives and attacks the Efrafan soldiers. Hearing the commotion, Woundwort abandons Bigwig and fearlessly confronts the dog. No trace of Woundwort is found, leaving his fate ambiguous.
Several years later, the warren is thriving. An elderly Hazel is visited by the Black Rabbit of InlÃ©, who invites him to "join his Owsla", assuring him of Watership Down's perpetual safety. Reassured, Hazel accepts and dies peacefully. Hazel's spirit follows the Black Rabbit of InlÃ© through the woodland and trees towards the Sun, which metamorphoses into Frith, and the afterlife.

Question: What led to food shortage?
Answer: The Rabbits eventually multiplied and their appetite lead to a food shortage.