Cannot read property 'location' of undefined in React Router example

Trying to do the most simple example possible with React Router. Every example I've looked at is very different and many include 20 page tutorials. I just want a simple root path to work:

...
<script src="https://unpkg.com/react@15.3.2/dist/react.js"></script>
<script src="https://unpkg.com/react-dom@15.3.2/dist/react-dom.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.23/browser.min.js"></script>
<script src="https://npmcdn.com/react-router/umd/react-router.min.js"></script>
...

var insert_point = document.querySelector('#container');

var App = React.createClass({
  render: function() {
    return (
      <div>
        <h1>Simple SPA</h1>
        <ul>
          <li>Home</li>
          <li>Stuff</li>
          <li>Contact</li>
        </ul>
        <div>
        </div>
      </div>
    )
  }
});

ReactDOM.render(
  <ReactRouter.Router>
    <ReactRouter.Route path="/" component={App}>
    </ReactRouter.Route>
  </ReactRouter.Router>,
  insert_point
);