Many pagan/non-Christian societies had/have a god of war. Ares was the Greek god. The gods of war of other societies were/are:
Agrona (Celtic Britain)
Alaisiagae (Norse)
Annan (Ireland)
Andraste (Anglo-Celtic)
Ankt (Egypt)
Ares Enyalius (Sparta)
Astarte (Semitic)
Athena (Greek)
Badb (Irish)
Bast (Egypt)
Beda (Romano-British)
Belatu-Cadros (Northern Britain)
Bellona (Roman)
Bishamonten (Japanese)
Boudihilia (Romano-British)
Brahma (Hindu)
Brigantia (Gallo-Roman, Germanic, Romano-British)
Brigid (Ireland)
Bugid Y Aiba (Haiti)
Camulus (Celtic)
Cariocecus (Lusitania)
Catubodua (Celtic Gaul)
Chi You (China, Korea)
Cocidius (Northern Britain)
Durga (Hindu)
Eckchuah (Mayan)
Enyo (Greece)
Esus (Gaul)
Ffraid (Scotland, Wales)
Hachiman (Shinto)
Hadúr (Hungary)
Hanuman (Hindu)
Honos (Roman)
Huitzilopochtli (Aztec)
Iktinke (Lakota)
Indra (Hindu)
Kali (Hindu)
Kukailimoku (Hawaii)
Laran (Etruska)
Maahes (Egypt)
Macha (Ireland)
Mandarangan (Philipines)
Mars (Rome)
Menhit (Nubia, Egypt)
Menrva (Etruscan)
Menthu (Egypt)
Mextli (Mexican)
Murugan (Hindu)
Mórrígan (Ireland)
Neit (Ireland)
Neith (Egypt)
Nemain (Ireland)
Nike (Greece)
Odin (Germanic, Norse)
Ogoun (Yoruban, Haiti)
Oro (Tahiti)
Perun (Slavic)
Pikullos (Prussia)
Resheph (Mesopotamia, Egypt, Phoenician)
Ricagumbeda (Celtic)
Rudianos (Celtic Gaul)
Samulayo (Fiji)
Satis (Egypt)
Segomo (Celtic)
Sekhmet (Egypt)
Set (Egypt)
Smertios (Celtic Gaul)
Sopdu (Egypt)
Takemikazuchi (Shinto)
Tanit (Phoenician, ancient Egypt, Berber)
Teoyaomicqui (Aztec)
Zezcatlipoca (Aztec)
Thor (Germanic, Norse)
Tumatauenga (Maori)
Trebaruna (Lusitania)
Tyr (Germanic, Norse)
Vacuna (Roman)
Victoria (Roman)
Woden (Germanic, Norse)
Zhanshen (China)