For a few years in the 1960s, Elsa the lioness was the most famous animal alive.

Raised by humans after her mother's death, she was eventually released back into the wild. Her story, which was made into a successful film, inspired thousands of people to become involved in wildlife conservation.

Elsa's home was Meru National Park in Kenya. At the time, Meru was a glorious wildlife haven, home to thousands of large animals including many lions. But in the years after Elsa's death, the park was overrun by poachers and its wildlife was almost wiped out. Only in the last few years has it begun to recover.

This is the story of the savage battle for Meru National Park: a fight that was inspired by the story of Elsa the lioness.

Meru National Park is wild and rugged, spanning an area twice the size of the Isle of Wight. It was once a showcase of environmental diversity. Its grassy savannahs supported vast herds of buffalo and zebra, alongside elephants, lions and leopards.

Elsa survived for several years and reared three cubs

In the 1960s the park became internationally famous. That was thanks to Born Free, a bestselling book by Joy Adamson. It recounted the true story of how Adamson raised an orphaned lioness cub named Elsa.

In 1956, Adamson's husband George shot Elsa's mother when she charged him. He realized afterwards that she only did so to defend her cubs, and so he and Joy decided to raise the young lions themselves.

Joy was determined to teach Elsa to survive on her own, and eventually released her into Meru National Park. Elsa survived for several years and reared three cubs, before dying of a tick-borne disease in 1961.

Elsa's story played a large role in pushing lion conservation, and that of all wildlife, onto the international agenda.

Within a few years of the release of Born Free, Meru's heyday came to a devastating end

It also helped Meru become one of Kenya's most important conservation sites. Tens of thousands of tourists piled in each year to see the abundant wildlife.

Elsa's story was retold in the Oscar-winning film adaptation of Born Free, which was released in 1966: 50 years ago this year.

British actors Virginia McKenna and Bill Travers, who were married in real life, played Joy and George in the film. The actors were so affected by the experience that they established a charity, the Born Free Foundation, dedicated to the welfare of wild animals.

As a result, Elsa's grave, which is set under a giant fig tree on the banks of a river, became a symbol for the wildlife conservation movement. But today, her grave hardly receives any visitors.

Within a few years of the release of Born Free, Meru's heyday came to a devastating end.

Our rangers used to confront the poachers, but when firearms became machine guns they were overpowered

The park is situated in a volatile area of Kenya, next to two troubled countries: Somalia lies to the east and Ethiopia to the north.

The conflict started with the Shifta War in the 1960s, when ethnic Somalis in north-east Kenya fought to have their lands become part of Somalia. A ceasefire was eventually declared, and in 1967 the war ended.

But the region remained insecure, a situation exacerbated by the ongoing conflicts in Ethiopia and Somalia. Then militias bearing automatic firearms entered the fray.

"Most of the region was unstable," says Tuqa Jirmo, the Park's senior warden. "Meru was caught in between."

Elephant and rhino tusks were being sold, and people ate the other animals

Meru's park rangers only had clunky shotguns. They­ could not cope.

"[The militia] had machine guns, not just bows and arrows like before," says Jirmo. "Our rangers used to confront the poachers, but when firearms became machine guns they were overpowered."

At the same time, there was a growing demand for ivory in Asia. This made poaching an attractive source of income for poor people. So Meru's animals began to be shot dead.

"Elephant and rhino tusks were being sold, and people ate the other animals," says Jirmo. "There were so many elephants that no one thought they would become endangered. Conservation wasn't a great issue."

By the late 1970s, Meru was a poachers' playground, and for the next decade it was essentially lawless.

Any ranger who stood up to the poachers was likely to end up dead

The park's infrastructure was ruined, and poor roads made most of it unreachable. The impassable bush made Meru the perfect poaching ground, and its wildlife was massacred. Jirmo calls it "a no-go zone".

Elephant populations dropped from over 3,000 to a couple of hundred. Rhinos went from numbering almost 100 to being completely wiped out. The hundreds of lions that had once roamed the park were decimated.

Kenya's Wildlife Conservation and Management Department tried to stop the poaching, but it was hopelessly inefficient and short of cash.

Part of the problem was that the rangers were reluctant to put their lives on the line to protect wildlife. They had good reason to be unmotivated: their wages were poor, and their weapons were feeble compared to those of the poachers. Any ranger who stood up to the poachers was likely to end up dead.

In 1980 Joy Adamson was found dead, and it later emerged that she had been murdered

After several rangers were killed by poachers, the survivors chose to stand aside and not interfere.

"Rangers didn't challenge the poachers, so they basically had free realm over this area," says Tim Oloo of the Born Free Foundation.

This eventually became brazen. "There were five white rhinos and the bandits sent word saying they were coming to kill the rhinos, and they came and did it and left with their horns," says Oloo. "No one did anything."

The park had also lost one of his foremost champions. In 1980 Joy Adamson was found dead, and it later emerged that she had been murdered.

The last straw came in 1989. Bandits killed two French tourists in Meru, and a month later George Adamson was murdered in nearby Kora National Park. Meru closed its gates, and the story seemed to have come to a crushingly sad end.

But in 1990 the government launched the Kenya Wildlife Service. It took over from the Wildlife Conservation and Management Department, which had so utterly failed to protect Meru.

For the next decade, the newly-energised rangers fought a running battle against the poachers

The first step was to restock the park. Helped by $1.25 million from the International Fund for Animal Welfare, Meru brought in more than 1,300 animals from other parks over a period of five years. The new inhabitants included rhinos, giraffes, impalas, leopards, zebras, elephants and black rhinos.

At the same time the roads were repaired and lodges were built for visitors.

Crucially, the rangers were given proper security training, automatic guns and state-of-the-art radios – as well as improved salaries and housing.

For the next decade, the newly-energised rangers fought a running battle against the poachers. Gradually, the bandits were driven out, and Meru began to come back from the brink.

In February 2016, Meru conducted its first lion census

Today, poaching remains a threat, but it is no longer a massacre. Instead, a poacher-proof rhino sanctuary protects 60 rhinos, which are monitored 24 hours a day. In 2014 two armed poachers tried to kill a white rhino, but ended up shot dead themselves.

"We are still in a volatile area, but poaching is not that bad," says Jirmo.

The park is once again home to many large animals, as well as more than 400 bird species. But Elsa would not recognize it, for there are hardly any lions.

In February 2016, Meru conducted its first lion census, which revealed that there are only about 80 lions in the entire park. Meru's lion population is desperately low.

Someone will intend to catch buffalo and an elephant will fall victim

This parallels lions' decline throughout Kenya. Only 2,000 remain in the entire country, compared to the 100,000 that lived there in Elsa's day.

Still, there is hope Meru will become lion country again.

"The census is the first step," says Jirmo. "Next we can get to know the individual lions, monitor and track them. In the coming years this place will go back to the way it used to be."

But before Meru's team can achieve that, they must first solve the park's biggest remaining problem: snaring.

Snares are deadly wire nooses. People place them in the bush to catch animals for their meat, which they may either eat themselves or sell on.

The poor communities on the perimeter of the park are struggling to make a living

"They target buffalo, giraffe, impala, but the major problem with the snaring is that it is indiscriminate," says Victor Mutumah of the Born Free Foundation. "Someone will intend to catch buffalo and an elephant will fall victim."

There have been successful prosecutions but these are only part of the solution.

"People are getting sentences for killing the animals," says Mutumah. "But unfortunately most of the damage will already have occurred and animals will have gone through a painful death."

The root of the snaring problem, Mutumah says, is that the poor communities on the perimeter of the park are struggling to make a living, and they have a troubled relationship with its animals.

Elephants from the park trample their crops, while lions and cheetahs kill their livestock. This means local people have negative attitudes to wildlife that are hard to change.

They come and tell us when someone is snaring

"For many people, conservation is not their priority," says Mutumah. "They need to feed their families first."

Worse, many local people see the safari parks as the preserve of rich tourists. It only costs Kenyans 350ksh (£2.50) to enter the park, but hiring a vehicle to get around in costs much more. As a result, most locals have never visited.

"People don't think there is any direct benefit to them from the parks," says Mutumah.

Now Meru is trying to help the community. It contributes to education, healthcare and water facilities, and takes schoolchildren on game drives to help them feel involved.

Many people still think Meru is not safe, and without tourists visiting there is no revenue

"There has been a serious engagement with the community," says Mutumah. "They take the issues of Meru more seriously because they are able to relate with it in some way."

Crucially, "they come and tell us when someone is snaring," he says. "We have seen a drastic reduction in the number of snares but a lot more needs to be done."

Throughout this saga, the Born Free Foundation has been absent from Meru – even though it owes its entire existence to the park.

The Born Free Foundation was founded in 1984. At first it was called Zoo Check, and it focused on the welfare of captive animals in the UK.

Then in 1998 the charity expanded its remit to all animals. It began work in Kenya, but it did not enter Meru. While the rangers had started to fight back against the poachers, the park was still too dangerous.

We really needed to come back and continue what George and Joy did back in the day

It was only in 2014 that Born Free finally began came to Meru National Park. Their aim: to help return it to its former days. As a first step, they have retrieved more than 1,600 snares in two years.

"A lot of work needed to be done here," says Mutumah. "Many people still think Meru is not safe, and without tourists visiting there is no revenue."

Indeed, even now only about 3,000 tourists visit each year, and Meru relies on more profitable parks like the Maasai Mara to keep going. That will have to change if it is to survive in the long term.

"We really needed to come back and continue what George and Joy did back in the day," says Mutumah. "This is where we began."

If all goes well, in another few years Elsa's grave will receive far more visitors than it has in decades – and a new generation of lions will thrive where she once roamed.

Join over five million BBC Earth fans by liking us on Facebook, or follow us on Twitter and Instagram.

If you liked this story, sign up for the weekly bbc.com features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.