break the back of

verb3

1. •
   To overburden (a person, group, or organization).

   • You will have heard of the three kathia system. It broke the back of the farmers. — 1962
2. •
   To cripple.

   • The Russian intervention then broke the back of IS in north-western Syria enabling the knockout blow to fall on Raqqa in October 2017 as this was the last stand of IS. — 2021
3. •
   To complete the greater part of (a project) or solve the most critical part of (a problem).

   • I've broken the back of painting the shed – I'll finish it after lunch.