Board Thread:Lore Discussion/@comment-26357188-20150504050710/@comment-173.81.113.240-20170128002510

Essentially yes, Daedric Princes can invade other realms. The Greymarch is an excellent example because during that time Sheogorath had returned to being Jyggalag, this is practically two realms attacking each other. One Prince pitting their forces and influence against another, normally when these types of conflicts happen, the two Princes would cancel each other out or cause massive devastation that would have to be repaired. But its the likelihood of the cancelling each other out that makes the Princes use human proxies to fight in Nirn for them for their own safety.

Meridia and Molag Bal fought against each other, Bal attempted to invade a city under Meridia's control and she was able to transport it into his realm. This undermined Bal's influence in his own territory, a place where he cannot see or influence. Though the two didn't actually meet face to face in combat or their forces in Oblivion, its still possible for them to do that. Nirn just happens to be a convinent and, ironically, safe battlefield.