What separates the US and Russia leads to each saving energy (6,3)
I believe the answer is:
bering sea
'what separates the us and russia' is the definition.
'leads to each saving energy' is the wordplay.
'leads to' becomes 'brings'.
'each' becomes 'ea'.
'saving' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'brings'+'ea'='bringsea'
'bringsea' going around 'e' is 'BERING SEA'.
(Other definitions for bering sea that I've seen before include "Water between Russia and Alaska" , "deep water?" , "lot of cold water" , "the Russian border being fluid" , "Northern waters" .)