Some Puranas mention twelve wars between Gods and Demons. Unfortunately, some details are missing.
Amritamanthana War – Fought for Amrita.
Varaha War – Killing the demon Hiranyaksha. Vishnu’s Varaha, Boar, Avatar.*
Narasimha War – Killing the demon Hiranyakashipu. Vishnu’s Narasimha, Manlion, Avatar.*
Vamana War – Killing the demon Bali. Vishnu’s Vamana, Dwarf, Avatar.*
Jita War – Decimating the Kshatriyas. Vishnu’s Parashurama, Rama with the Ax, Avatar.*
Tarakamaya War – Abduction of Tara.
Ajivaka War – No details found.
Tripuraghatana War – Shiva destroys Tripura.
Andhaka War – Killing of the demon Andhaka.
Vritrasambhara War – Indra kills the demon Vritra.
Kolahala War – No details found.
Halahala War – The poison Halahala appeared during the churning of the ocean. Halahala is personified as a demon. Shiva drank the poison. Vishnu killed Halahala and saved Shiva.
*For the stories see Dashavatara.