I always thought 1964 and 1972 were aberrations. Not only did the losing candidate really lose big, but the issues were unusual in those years, so the normal patterns didn't necessarily apply then. As recently as Dukakis and Clinton, Democrats did very well in a lot of rural areas.
I trace the modern red state/blue state divide to the spittle wave of 1994. Although the country generally trended to the far right, the urban areas recovered by 2000. The rural areas did not.
I think you mean the suburban areas. The urban areas were very Democratic even in 1994.