This comes in two parts - killing LA and making Chicago boom.
1) Bumping off the competition; to make Chicago #2, just bump off LA.
Mid-Century everybody thought LA would be the city of the future, but the Quake of 64 ended that. In fact the quake was so severe it throw the entire nation into recession even though less than 10,000 people actual died in the quake. The immigration reform act of '65 was shelved and measures were taken to prevent Mexican immigrants from grabbing scarce post-quake jobs.
LA seemed on the mend when race riots hit LA in '68 following the assassination of Martin Luther King. This lead to white flight and the city's biggest booster the LA Times selling out to a national newspaper chain. SoCal lost the aerospace wars with Grumman (Long Island NY) and McDondald-Douglas (St. Louis). Environmental regulation has restricted industry in the LA basin. Still, LA has rebounded in the last 20 years. It being 50 years since the big one has hit, LA is making a comeback based on its great weather and is now the 8th largest city in the USA.
2) People come to Chicago for the good jobs not the weather, so lets turn some also-rans into superstars.
Chicago's transition from the blue collar "City of Broad Shoulders" to the modern day white collar mecca "Chi-Town" was not an easy one. Some credit has to go to Mayor Daley Sr. who prevented Chicago from turning into another Detriot in the 60s and 70s. Chicago, while remaining the second largest city in the country, declined in population for a generation until the boom started post 1990 recession. Then much like NYC Chicago saw a remarkable, if economically uneven turn around.
However the most credit has to go to the nerdy number crunchers at the University of Chicago Business School (perhaps the best quant B-school in the country) combined the marketing geniuses at the Northwestern Business School Kellogg (again perhaps the best Marketing B-School in the country).
They are credited with the turn around of Sears as well as the spectacular rise of Motorola.
In the early 80s Sears and its traditional downscale rival K-mart were facing a new type of competition - companies such as Home Depot using the "Big Box" format. Not understanding what they were facing Sears simply bought out one of its competitors a respectable and growing chain based in the Twin Cities known at the time as Target. It wasn't until after the purchase did the quants convince the Senior management that the Big Box Store, aided by advances in computer inventory, was the wave of the future. Sears became quite the convert and now battles with its downscale rival Walmart for the biggest piece of the nation's retail pie. Sears in Chicago is famous of course for the tallest building in America, the Sears Tower, which despite the skeptics more than paid off for Sears as most of its operations can be centralized in one building.
Motorola is cellphones. It is also a fortune 10 company that pumps the more money into the Chicago economy than whole sectors such as traditional mainstays like transportation and food processing. Its success made Chicago the world wide leader in the booming telecommunications industry. People worry that Chicago's success is too tied up with the success of Motorola since there are some storm clouds on the horizon. People worry that the Steve Jobs newly created iphones will steal the thunder from Motorola's marketeers and technologist. Also although Motorola has so far survived anti-trust actions in the US, investors worry that the latest EU anti-trust moves (brought on by an obscure Finnish manufacture Noika) might seriously damage Motorola's future prospect.
Although Chicago has not truly shaken off its "Second City" status , its long rivalry with New York continues as its rivalry now plays out on an international stage. Both cities are considered the leading global cities of the USA.