Don't they also actively destabilize each other though? I'm not sure why this should be considered the primary cause behind it.
I mean, look at Ethiopia. Forget Western powers, Ethiopia has never been successfully invaded by any foreign power. Despite this, it is one of the poorest countries on the planet today.
It seems to be the prevailing theory that any misfortune befalling these countries is due primarily to the west.
These countries would be thriving without western interference is the claim.