Originally posted by WhimpyCiv
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So it is the attack and not just the declaration of war that triggers an MPP?
-- WC
It's not just an attack, just staying (respectively ending up a unit'S turn) on foreign territory triggers MPP. So if you move troops on foreign turf (not actually attacking, just ending movement in there)
and are in a state of war with that civ, you'd get a war declaration from your foe's MPP partner.
Same with bombing, pillaging and capturing - as long as such hostile action takes place on the territory of a civ that has signed a MPP.
Note: The troops-on-foreign-territory-thing can get very annoying if your foe signs a MPP with another civ in the middle of the war. Depending on the playing order, it could happen that such a MPP gets triggered 'immediately' (when your troops are actually staying on your foe's territory, of course). You'd get a pop-up like: "Civ X [your foe] signed MPP with civ Y [neutral towards you]" and directly after that: "civ Y declared war on us... blabla...because of MPP with civ X" during the inter-turn.
The playing order can be derived from the contact menue which shows up if you click on the "D" next to the info box: playing order is sorted from bottom to top.
about the attitude and reputation thing:
like Gainy said, you'd get a rep hit if you declare war while having troops on foreign turf (it's treated like a ROP-rape - whether you had a ROP or not).
Apart from that, your attitude could even get better after performing such a ROP-rape - that is, if some civ regards your foe as "common enemy" (they are at war that foe as well). That attitude boost is probably only temporary, though, while your rep is trashed for the rest of the game...