Except that America stirred up this issue only because it was done by a rich American. Zimbabwe aided by claiming it was an illegal poaching, arresting the guides and then asking America to arrest and extradite Walter Palmer.
Lions are scary when they aren't in a national park and being monitored by research scientists, but that's not what happened. This would be like a foreign tourist luring a wolf out of Yellowstone and then killing it outside of the park boundaries. It's straight up illegal poaching.
Saying that someone committed a crime is a Big Deal. In many jurisdictions, it is considered slander or libel unless you are making a formal charge. You need something a lot stronger than something you read in a newspaper to back it up.
This is what people understand - Lion Conservation status: Vulnerable
"The lion is a vulnerable species, having seen a major population decline in its African range of 30–50% per two decades during the second half of the 20th century. Lion populations are untenable outside designated reserves and national parks. Although the cause of the decline is not fully understood, habitat loss and conflicts with humans are currently the greatest causes of concern."
They dont own the Lions, the Lions happen to live within the same lines drawn on a map as they do. The Lions neither know about or care about these lines. That in no way makes these Lions the propery of people from Zimbabwe.
In the same way that the rainforest destruction is everyones problem, not just a problem for those living in the rainforest.
Also the world hardly operates according to that concept of owning that you mention with regards to environmental protection. Is the international community pledging resources to support countries that choose to protect the environment instead of seeking so-called economic development? See for example this https://en.wikipedia.org/wiki/Yasuní-ITT_Initiative
Isn't this due to the explosion of human population levels though? We're encroaching more and more on the natural habitat of pretty much every species on the planet except for those in the deep ocean and even they are affected by us in other ways.
There are several issues. Not just one.