Samatha Powers of Time magazine (previous link) has all sorts of nonsensical reasons why no one could invade and overthrow Mugabe.
Her main reason is ideological, as seen by her ridiculing of "neocons" in the middle of her essay.
Nope, suffering people don't count, only politics does.
However, she might want to read about when one African country actually did overthrow a tyrant.
The bad news: Because no one wanted to mop up the problem, things got worse in many ways.
The lesson of the US in Iraq is that no one wants to stay the course to establish democracy (although this year things seem to be turning around).
And the other lesson is that good leftists prefer to hate America (especially with a president who is republican) than to love Africans.