what is { Break the back of the beast } ?
"After hours of effort, the technicians finally broke the back of the beast
and turned the electricity back on again."

Question

what is { Break the back of the beast } ?
"After hours of effort, the technicians finally broke the back of the beast
  and turned the electricity back on again."

Answer

"To break the back of the beast" means, literally, that you conquered the beast (breaking one's spinal is kind of a final thing for most Vertibrates). So, metaphorically it means: to be 'victorious' solving a large and/or difficult job (as if you battled a large animal).

Answer

this may mean taking a crowbar and killing the evil wolf who attacked you )

Answer

The "beast" is figurative, meaning a thing, a problem or a situation that must be brought under control.

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