balance of power
noun [ S ] uk/ˌbæl.əns əv ˈpaʊər/ us/ˌbæl.əns əv ˈpaʊ.ɚ/
（通常指政治）力量均衡
a position in which both or all of the groups or people involved, usually in a political situation, have equal power
Both countries have a vested interest in maintaining the balance of power. 两国在维持均势上都有着既得利益。
Idiom
hold the balance of poweridiom 举足轻重，掌握决定权
to be able to support either opposing side in a competition, etc. and therefore be able to decide who will win
If independents do end up holding the balance of power, then they decide whether Labor or the Liberals govern for the next four years. 如果无党派议员果真取得了举足轻重的地位，那么他们将决定由工党还是自由党来组成下一届四年期政府。