In this quatrain from Owen Seaman's poem "Pro Patria," what does the word just mean?

England, in this great fight to which you go
Because, where Honour calls you, go you must,
Be glad, whatever comes, at least to know
You have your quarrel just.

A.
that the war that England faces has only recently begun

B.
that the soldiers will be proud to fight for their country

C.
that the English soldiers will face danger with honor

D.
that the soldiers are engaged in a war that needs to be fought