Why isn't block by block built on an adaptive?

Question

HTML

Tell me, I connected bootstrap.
Made a simple structure

<div class="contaiter">
<div class="row">
 <div class="col-xs-6"></div>
 <div class="col-xs-6"></div>
</div></div>

Why do I shrink the screen window and my blocks are compressed, and not stacked under each other ..
Tell me what I didn’t do .. or what needs to be done

Answer 1

xs is the smallest resolution. Change for example to md and to 991px width and less blocks will be under each other
See it on getbootstrap website