The Western powers had a lovely few hundred years of decimating native populations with their colonies, and then leaving in the night for their previously subjugated to fend for themselves with broken economies, weak leadership, and no institutions. Is it any wonder most of Africa and the middle east are in such shape?
While I can understand the point you make regarding all the issues in Africa, Middle East, etc, that statement in itself sounds rather simplistic to me, or even half mistaken even.
If these Western Powers "left in the night" it was also because most of those colonies actually thrived for their independence. It may seem that way for a lot of british colonies because the way the british commonwealth was done and worked. The emphasis was always put on the commonwealth and the merchant fleet, as well as trade. What the british did right was that their colonial overseers were not extremely intertwined with their colonies and their natives. Most transitions between british rule and local autonomy went more or less smoothly, if i'm not mistaken, and it was even a government will to actually go that way, which can give the feeling that they "left in the night". Except maybe in India, but that started out of local issues iirc.
If you take french colonial Empire on the other hand, the emphasis was put on very different matters, and most of them were either on triangular trade with slave trade (like everyone did) in the first colonial empire, but in the second colonial empire (which means the modern colonial empire, from which a lot of isles still remain part and fully integrated to the nation) the emphasis has always been on "uplifting" natives and bringing civilization and culture to these lands. Most of these have always been considered a very true and important part of the nation itself, nation that was supposed indivisible and united under a common cultural legacy. This spawned dirty wars like Indochina and Algeria among other conflicts (not real wars) less known, like New Caledonia. Which is also why the state has always kept its tendrils very deep in ex african colonies, and is still doing so.
Actually at the risk of sounding a bit imperialist, all those decolonizations were probably extremely detrimental to most of the newly formed countries afterwards. Especially in Africa with such arbitrary borders and the total loss of support from the metropolis. It should have been done more smoothly, as hastened as they were. In either way, these countries are left alone, or pillaged by westerners through widespread national corruption.