If you don't have time to read Greenberg's book, or Becker's, I suggest a recent essay by Greenberg, published in the online magazine Aeon. Greenberg's essay is titled, "This mortal coil," and is introduced by the following statement:
The fear of death drives many evils, from addiction to prejudice and war. Can it also be harnessed as a force for good?
As Greenberg describes his theory, "death thoughts" and "death salience" remind us of our mortality, and that makes us afraid. When we are afraid, our defense mechanism is to cling to whatever worldview we grew up with as children, or have adopted as adults. Thus, an "us against them" approach to life (accelerating conflict and hostility), derives immediately from a fear of death.
Why does a collective worldview like nationalism help us to "manage" the terror of our inevitable death? Because when we are faced with the inevitability of our individual demise, we calm our fears by telling ourselves that "we" are not really going to die and disappear forever. The group to which we have pledged our allegience (our nation, for instance) will continue after our individual death, and so our existence, as long as we remain faithful to that group, or worldview, will continue.
I am not completely sold on the idea that "terror management," as explained by Greenberg, is an effective technique that can be a force for good. Greenberg certainly does provide, however, an interesting explanation of why it is so common for individuals to cling to some perceived greater collective reality. Doing that serves to shield us, psychologically, from the inevitability of our individual disappearance from the world.
Greenberg doesn't give him any credit, but Greenberg's article makes me understand, from a new perspective, why Jesus was providing us such good advice when he said, "Fear not."