It stated in early Naruto that Zabuza attempted a coup in the Hidden Mist Village, but failed. This is interesting due to information disclosed much later in the series, mainly that
with his Sharingan, Tobi was manipulating the Mizukage.
However, the series gives us only occasional tidbits about the Hidden Mist Village's history. Is Zabuza's motivation for staging a coup ever explained in any of the various media? Did he know about Tobi and have a problem with that? Did he just dislike some policies the Mizukage was doing? Or did he want some particular policies? Was it just a power grab?