I think it would have a positive impact on America and the world if Africa was able to develop. For one thing, we would not have so many African refugees. We also would not have to spend as much time putting in basic infrastructure there and could focus on helping them develop more. Less violence and famine would definitely be good for the human race.
Development in Africa will not have a great impact on the United States until it gets to be a good deal more advanced. Development in Africa could affect the US in two main ways. First, it could reduce the amount that the US needs to spend on aid to Africa. Second, it could provide new markets for some American goods. However, to have a significant impact in either of these ways, development would have to progress much farther than it has to this point.