Because you did not obey the LORD or carry out His burning anger against Amalek, the LORD has done this to you today.
KJV
Because thou obeyedst not the voice of the LORD, nor executedst his fierce wrath upon Amalek, therefore hath the LORD done this thing unto thee this day.
ASV
Because thou obeyedst not the voice of Jehovah, and didst not execute his fierce wrath upon Amalek, therefore hath Jehovah done this thing unto thee this day.