Bill Gates at the website of the Gates Foundation:
I've heard this myth stated about lots of places, but most often about Africa. A quick Web search will turn up dozens of headlines and book titles such as 'How Rich Countries Got Rich and Why Poor Countries Stay Poor.'
Thankfully these books are not bestsellers, because the basic premise is false. The fact is, incomes and other measures of human welfare are rising almost everywhere, including in Africa.
So why is this myth so deeply ingrained?
I’ll get to Africa in a moment, but first let’s look at the broader trend around the world, going back a half-century. Fifty years ago, the world was divided in three: the United States and our Western allies; the Soviet Union and its allies; and everyone else. I was born in 1955 and grew up learning that the so-called First World was well off or “developed.” Most everyone in the First World went to school, and we lived long lives. We weren't sure what life was like behind the Iron Curtain, but it sounded like a scary place. Then there was the so-called Third World—basically everyone else. As far as we knew, it was filled with people who were poor, didn't go to school much, and died young. Worse, they were trapped in poverty, with no hope of moving up.
More here.