Neimoidia was colonized by Duros in the early days of the Republic. Over the centuries, the Neimoidians evolved into a totally different species. They did this in an attempt to circumvent the various anti-Duros laws. It didn't work. Neimoidia became the home to the Trade Federation- which was basically an elaborate protection scheme. This made the planet very rich. So rich that additional planets were needed just to store money. These became known as the Neimoidian Purse Worlds:
Neimoidia saw heavy combat during the Clone Wars. Afterwards, the planet was given back to Duro as reparations.