The black 5-pointed star had been a symbol of the Enarese people ever since they settled the lands of western West Alabar. When their territories were annexed by Dorland and Palissan, it became the symbol of their resistance and hopes for independence.
Eventually, an organization known as the Order of the Black Star was formed. It was willing to use violence to achieve its aims, and in fact it incited a war between Palissan and Dorland over the Enarese issue.
The main consequence of the war was the creation of an independent Enaroland, which naturally enough wanted to put the black star on the flag. Many people in Dorland objected, as it had recently been the symbol of a violent separatist movement. Of course, the fact that Dorland was against it was a good enough reason for Palissan - their long time rivals, who had inflicted a humiliating defeat on Dorland - to be for it.
So the flag of Enaroland is a tricolor, with blue stripes on either side, a white stripe in the middle, and a black star on the white stripe.