Angelina Hackmann, PhD student at the Working Group “quantitative Macroeconomics”, and Torben Klarl have published an article in the journal Papers in Regional Science on city size development in the U.S. between 1840 and 2016. The authors show that the city size distribution deviates from Zipf's law, especially in the second half of the 20th century. The city size distribution has become more even, which is mainly due to the fact that smaller cities have grown faster than larger cities. This can be explained, inter alia, by an increased importance of suburbanization processes since the 1960s.
This article is also available via the following link: https://rsaiconnect.onlinelibrary.wiley.com/doi/abs/10.1111/pirs.12498