His planet got hit with sanctions by the Republic, and it forced them into starving. Then the Banking Clan stepped in, telling him they'd bankroll the planet if he became what was essentially a glorified leg-breaker for them. He complied for a while, until the enemies he fought in the war came back and desecrated burial lands. So he abandoned his hitman gig, and went back to restart the war.
That's when Dooku and Sidious stepped in and decided to blow up his ship.