What is "softening up"

Usage examples of "softening up".

By the end of our trip this process would assume nightmarish proportions, by comparison with which our first entry into Zaire was a relatively gentle softening up process, and consisted of only two hours of rain and misery in huts.

An Imperial attack usually centered around heavily armored battle wagons and war machines, but the cold and the snow and the ice of Mistworld slowed them down too much, and most were too large anyway to maneuver in Mistport's narrow streets, so the softening up of the city fell to the Imperial air divisions.