You simply haven't closed the
<div>'s properly—please refer to the code below, where it says
<!-- NEW DIV CLOSING TAG -->.
If you are using CodePen, it is also worth noting that at the top-right corner HTML area, there is a small arrow where choosing "Tidy HTML" will, well, tidy your code up for you. If things don't line up after tidying up, there is a good chance that you are missing a closing tag somewhere.
I don't know if there is a solution within CodePen for automated cleanup of code, but I used to use DirtyMarkup when I just can't spot what's wrong.
I personally always close a tag, where necessary, as soon as I start one. If you need to copy and paste snippet of code, make it a habit to format it first before implementing it.
I hope that helps!
P. S. You can use triple back-ticks (`) before and after a code block to format it:
<h1 class="text-center">Kadir Suleymanoglu</h1>
<h2 class="text-center"><em>The Man, The Legend, The Reality</em></h2>
<img class="img-responsive img-thumbnail" src='//discourse-user-assets.s3.amazonaws.com/original/3X/1/5/15be7803556908ce7542708a2b524de33306696c.jpg' />
<div class="caption text-center">Exploring the skies of the Orient.</div><!--caption->
</div><!-- NEW DIV CLOSING TAG -->
<h3 class="text-center">Here's a time line of Kadir's life:</h3>