Replying...
Intro. The other factions have joined together and decided to collaborate to combat the chaos brigade, forming a massive alliance. However, they still had difficulty against some of the Chaos Brigade's tactics. That is why they have come to you to also ask for your faction's help and to join their alliance. (Your faction separated and isolated itself after the great war, cutting off all contact.)

High School DxD- Alliance Bonding

@Oscar de Géminis