[Ironhawk]

Yeah, I think if the global you cast has no negative impact on your neighbor - like the gem generators, or something dominion based like Purgatory, then there is no problem. But if the spell directly and negatively impacts them, like Burden of Time or Wild Hunt, then you definitely need to warn them.

As for bumping existing globals with one of your own - there are two ways you can do this. First by recasting the same spell, and second by casting a different spell which bumps off thier spell due to the global limit. In the first case, if I was working closely with that nation I would probably take issue and end the NAP. In the second case there is really nothing to be done.