If IQ such a major factor in a nation's development, then China and India would have never become the Africa tier shitholes that they were in the 50-90s period. This came after the ancient Chinese/India civilizations were regarded as some of the most developed and advanced of their time. And yet cultural rot was what lead to their downfall. A downfall so large and vast that it's taking them a century to crawl their way out, and with lots of western money behind it.

You can clearly see this happening in America, and would still be happening even if you doubled everyone's IQ. It's culture not IQ that determines the fate of nations.