History of Sprawl

I have an interesting question, What has the Federal Government done to facilitate sprwal from WW2 to present? I know they used heavy subsidation to acheive todays conditions, but I'd like more information on what they did and when. Why did this kill so many urban cores throught the rust belt? Anyone's input is greatly appreciated. Feel free to post any info you have inyour head or links to papers on this subject. Thanks Guys!>