Siege can destroy businesses (8)
I believe the answer is:
agencies
'businesses' is the definition.
(agency is a kind of business)
'siege can destroy' is the wordplay.
'destroy' indicates an anagram (I've seen 'destroyed' mean this).
'siege'+'can'='siegecan'
'siegecan' is an anagram of 'AGENCIES'.
(Other definitions for agencies that I've seen before include "Businesses that serve others" , "Businesses providing specific services" , "Administrative units of government" , "(Travel) offices" , "They organise transactions, between advertisers and media perhaps" .)