In the book 1984 by George Orwell how does the party claim war is peace?

Because the war is so constant and invasive, the people of Oceania have grown accustomed to it. It's comparable to a child who grows up living next door to a fire department- the sound of the fire sirens eventually lull her to sleep instead of disturbing her. Because there has always been and will always be war in this society, they see it as something normal, and the lack of it would upset the peace of consistency.