This is from the Bootstrap docs. By default each column is aligned/floated left, but with this the space in between the columns is equally distributed:
<div class="row justify-content-between">
<div class="col-4">
<div> Div 1 </div>
</div>
<div class="col-4">
<div> Div End </div>
</div>
</div>
It makes use of flexbox and there are several more options available to align your columns inside a row, or even wrap and nest them.
Read about it with this link: Bootstrap docs - Grid
With Bootstrap 4 there is another option for this. Because it makes use of flexbox you can add the .ml-auto to the last div in a row, but you should be wary of the overall row width (It should not exceed 12/12 columns widths). You can read anything about it in the Bootstrap 4 docs in the Layout/Grid section.