Let's define the IWP as "The International World Police" - the IWP. For any given single-human actor within an IWP, they then have to carry two sets of methods of accountability. One, to the nation-state they call home. Two, to the IWP.

The (military historical) literature is full of examples of this not working well. Making it Canada instead of the US, and using the UN as an IWP, the rules of engagement in Bosnia led to ... extremely widespread dissatisfaction.

I don't think an IWP is consistent with the mores and reality of the nation-state.