It's a really bad idea to execute asynchronous calls, i.e. AJAX, within the componentWillMount() method. Well, on the ReactJS site, they simply say not to do, but do not mention why. I know now!
I experienced an infinite loop of componentWillMount while making an AJAX call inside componentWillMount. Shifting the code from componentWillMount to componentDidMount resolved my problem instantly; but to get there I lost about three hours of my life.
UPDATE: This was not the real problem. See more here!