Complex sentence: The process of "blockbusting" was a national phenomenon, but nowhere was the practice of contract selling as pernicious as in North Lawndale, where an estimated 3,000 buildings were sold on contract.
Split into simpler sentences: The process of "blockbusting" was a national phenomenon. But, the practice of contract selling reached its peak in North Lawndale, where an estimated 3,000 buildings were sold on contract.