Assuming that you have spent the effort to develope more control over IAP (intra-abdominal-pressure, see here), or that you were gifted with the inherent ability to control IAP at will, which is the basic fundamental skill that must be applied to all of the exercises geared towards strengthening the lower back; the following entry is the intermediate stage on 'how to build a stronger lower-back".
↑ This diagram depicts a very common postural fault that is a result of modern life, which is spent mostly-seated. The hip flexors (iliopsoas) often stays shortened for prolonged periods when seated and remains inactive. Likewise, the erector spinae works overtime to balance the weight of the frontal part of the body, I.E. the arms, chest, head and objects held in the arms, thus making it tight and fatigued. Meanwhile, the hip extensors (gluteus muscles) are chronically overstretched, again due to the prolonged sitting, rendering it an overstretched and weak. At the same time, the abdominal muscles (especially transversus abdominus) are inhibited due to external factors such as: abdominal visceral fat accumulation, inactivity and chest-breathing pattern.
So should we all just stop sitting?
Maybe, if your daily life tolerates it. If you can get a standing workstation or if you ditch the life on the couch, then yes. These are simple solutions that will work, but will only fix half of the problem, because often times, the tight muscles have already adapted to a shortened length and the weak muscles have permanently lost its contractile strength and endurance that it once had. The result is a standing posture just like the diagram suggest, a duck butt and an overhanging belly.
The long term solution is to reverse this chronic weak-tight relationship in the lower trunk and re-stabilize the musculature to a more appropriate strength, aka core-strength, on top of the strength incorporated from IAP (intra-abdominal pressure).