Assuming you are using bootstrap 3. I achieved the effect that I think you need, nested columns:
<div class="col-sm-6"> <div class="col-md-6">A <br/> B <br/> C</div> <div class="col-md-6">D <br/> E <br/> F</div> </div> <div class="col-sm-6"> <div class="col-md-6">G <br/> H <br/> I</div> <div class="col-md-3">J <br/> K <br/> L</div> </div>
Demo
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