Actually, it isn't just Chicago. Murder rates are way up in all major U.S. cities lately, and nobody is quite sure why. They're still way down from their peaks decades ago, but it's a troubling trend.
I happen to be close with some people who prosecute violent drug gangs, and one trend they've seen is that mobile phones and social media have basically thrown gasoline on conflicts. It used to be that people had to be in the same place to start a feud, and most people were generally smart enough to avoid being physically in the wrong territories. Now you have people getting into it on Twitter and Instagram (not so much facebook), posting Youtube rap videos dissing each other, and things get out of hand.
Also, it's very easy for people to locate each other and assemble a crew for a shooting. In a way, it's sort of a trickle-down version of the command and control revolution that happened in the U.S. military in the late 80s and 90s. Technology give you real time intel and real time communication with your entire organization.
Finally, technology has had a cultural impact. It was always hard to raise a kid in these communities where there are powerful cultural elements that glorify violence, but now that stuff is hitting kids 24/7. All of these criminals promote themselves with social media and youtube videos, and kids are exposed to it even in the home.
Also, I think Black Lives Matter has something to do with it. I'm not sympathetic to the notion that police are now afraid to be proactive. Frankly, I think it's a good thing that police now feel like they need to be careful that their actions will be recorded and second guessed by everyone in the nation. But on the other hand, I think that heightened anger and resentment towards law enforcement leads to disrespect for the law. (Which is NOT to suggest that the anger is unjustified, just that it also has negative consequences.)