Learner's definition of HIGH GROUND
the high ground
: a position in which you have an advantage over others — often used in the phase the moral high ground
These countries lost/ceded the moral high ground [=they stopped being morally better than others; they lost the right to consider themselves morally better than others] when they entered the war to protect their economic interests.
She believes she has the moral high ground on this issue. [=she believes her position on the issue is the morally correct one]