Newswatcher,
I often fly AA to US cities from the UK via Chicago. Your schedule looks a little tight to me but I think Mark Lewis has it right - if your flight is booked with AA they should sort it out if you can't make the connection. A typical connection for me is two hours at ORD and I've not yet missed a flight, but that's no guarantee.
If you haven't gone via ORD before then I recommend trying to familiarise yourself with the inter-terminal transport beforehand. Once you've picked up your luggage and gone through immigration and customs you'll need to drop it off right afterwards. They've not screwed up my luggage so far so suspect you can do this with confidence.
Once you get beyond immigration and customs you suddenly find yourself in the USA. Head up the escalator in front of you and get on the train. You get off at terminal 3 and then go through security again. The whole process takes an hour typically, but it can hinge on if you're unlucky enough to arrive at the same time as five other international flights. I think you'll be OK though. Good luck.