what would America be like if 400, 000 blacks were not brought over as slaves.?

Peaceful, prosperous, productive, united

Nothing would have gotten built.

Let's see.  If Mr Peabody will let me use the WABAK machine I'll go back and personally stop all slaves grom coming to the North American Continent...  Just hang on a few minutes and with that little change in history, we can see what happens.  ===  OH, MR. PEABODY!

It's pointless to imagine a world that will never be. Silly wignats and their John Lenin 'nationalism.'

Ask the same question about the Caribbean, Brazil. Or, the Arab lands and Ottoman Empire. Except the impact of the latter would be different as even though they bought slaves in significantly greater numbers, they worked nearly all of them to death before they could reproduce.