User blog comment:B214/General Discussion/@comment-29963364-20161028202621/@comment-9595671-20161030220536

Maybe that's another reason Shiva's getting Issei's favor, if certain people side against Indra then he's likely not gonna wanna go for his planned war. The fact he wants it as his tournament prize implies he thinks he has a chance to beat Shiva.

And luckily, the EX timeline seems to imply that Indra never got his war. Either the above happened, Issei's actions in the arc made him realize killing him would do more harm then good (very unlikely though) or he realized stopping the war with the UL was more important.