Nuclear proliferation (4,4)
I believe the answer is:
arms race
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nuclear proliferation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for arms race that I've seen before include "Weapon competition" , "military competition" , "Weaponry competition" , "International competition for weapons" , "rush to war" .)