Wars in Heaven

How can heaven be a happy and a peaceful place when wars have been declared in the kingdom of God too? In Rev. 12:7 - 9: “And there was war in heaven: Michael and his angels fought against the dragons; and the dragons fought against his angels. . . And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast with him.” For my part, I ask: what was the devil and his dragons doing in heaven to begin with? Who created those celestial monsters, and for Christ’s sake, for what divine purpose? Poch Suzara