The lines hint at war. What information regarding the war is given at the beginning of the passage?

In the first paragraph, we learn that Ireland is in the midst of a civil war. Our specific setting is Dublin.

Around the beleaguered Four Courts the heavy guns roared. Here and there through the city, machine guns and rifles broke the silence of the night, spasmodically, like dogs barking on lone farms. Republicans and Free Staters were waging civil war.