This is a very short summary of the issue. In Kenya the elephant population decreased from about 160,000 in the 1960s to about 16,000 in 1989. That leaves only about 10% of the population. Why? Essentially all because of illegal poaching, to sell the tusks for ivory in the international market. Rhino poaching has been a similar problem.
Now with tougher laws and additional ranger surveillance the poaching has decreased dramatically in more recent years, but it is a constant fight. Why is it so hard to combat? Mostly because kenya is so poor and the indigenous peoples, mostly good people, are very poor. As one man says he doesn't sleep well because every day he worries how he will provide for his family.
So here's this giant herd of elephants, what is the problem with killing one of them and selling the tusks to support his family? That is the thought process which has made it hard to convince the locals to preserve the elephants.
This film is a documentary, the filmmaker spent time in Kenya to get to know the people, so they would trust him. What he made is a film with two parallel stories, one which follows the poachers to accomplish a job an unnamed merchant wants. The other is following the rangers who are hired to shoot to kill if necessary to stop poachers. It is clear that the poachers are very aware of the rangers and take great care to not be discovered which often means abandoning a hunt.
This is not a "slick" film, it is a realistic and authentic look at the issue, showing both sides. I found it very worthwhile viewing. I watched it at home on DVD from my public library, it has a couple of interesting extras on making of the documentary.