What caused Suburbia and stroads to form?

I'm working on a video that'll show a Minecraft village go from walkable to (horse) car-centric.

A big part of that is going to be the formations of suburbia and man-defying stroads. What I can't find a clear answer to is why these formed in the 1950s onward. Why did both the government and citizen population in Canada and the U.S decide this method of city planning was superior?