Bootstrap 3.3.7 "row" causing horizontal scroll bar

First of all you don't need row or col-*12 classes if your section is 100% wide look at this bootstrap example they have not taken any row or col-*12 neither with header nor jumbotron. If your section has column Just take row inside col-* classes for example

<div class="col-sm-6">
    <div class="row">stuff</div>
</div>
<div class="col-sm-6">
    <div class="row">stuff</div>
</div>

Fiddle

Or in case if you are using container-fluid

<div class="container-fluid">
    <div class="row">
        <div class="col-sm-6">
            <div class="row">stuff</div>
        </div>
        <div class="col-sm-6">
            <div class="row">stuff</div>
        </div>
    </div>
</div>

Fiddle

If someone is facing this in Bootstrap v4. Just add m-0 to your div.

<div class="row m-0"></div>