Ruling harshly is spoken of as ruling with an iron rod. Alternate translation: "He will rule them harshly as if striking them with an iron stick" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Breaking them to pieces is an image that represents either 1) destroying evildoers or 2) defeating enemies. Alternate translation: "He will defeat his enemies completely as if breaking clay jars into pieces" (See: [[rc://en/ta/man/translate/figs-simile]])