Parse error: Adjacent JSX elements must be wrapped in an enclosing tag

 React will not let you render two adjacent components unless you wrap them inside a div. This has a downside: your app may contain a lot of wrapping divs.

ReactDOM.render(
  <div>
    <App1 />
    <App2 />
  </div>,
  document.getElementById('root')
);

To avoid this issue, you can make use of the short syntax of the Fragments API which is included in React. 

ReactDOM.render(
  <>
    <App1 />
    <App2 />
  </>,
  document.getElementById('root')
);

That's it! no more dirty markup nor error messages :)