About 25,000 years Before the Battle of Yavin (BBY), the Duros species were one of the first sentient species in the galaxy to develop hyperdrive. With FTL techonology in hand they sent out colony ships, one of which colonized the planet Neimoidia. By 10,000 years after settling Neimoidia the damper climate and heavier gravity found there caused the Neimoidians to become physically distinct from their Duros parent species.
While the Duros were a gregarious people focused on exploring the galaxy, the Neimoidians focused their energy on making profits. The Nemoidians took over several nearby worlds, making them Purse Worlds. Neimoidians had a natural gift for calculations, which caused them to assess the risks in every action. This was seen by other species as cowardice, however the Neimoidians saw it as a critical survival skill.
Neimoidians were born as small grubs that lived in communal hives. They were forced to spend the first seven years of their lives in these hives competing for limited food supplies. Those who did not die within the first seven years but did not eat a sufficient amount of food in the first years of their lives became worker drones, while those that did survive grew up to become adult Neimoidians. These conditions made the survivors resourceful, but also made the survivors cowardly and greedy. Neimoidians also tended to be paranoid and always feeling that others were out to wrest their power away from them.
In addition to drones, the Neimoidians also relied quite heavily on droids to do their dirty work for them, fielding large armies of battle droids.
About three centuries BBY, the Neimoidians helped found the Trade Federation in order to gain wealth and spread their influence throughout the galaxy. Thirty-two years BBY the Neimoidians had allied themselves with the Sith Lord Darth Sidious, who had them invade his homeworld of Naboo in order to force a crisis in the government, and from there give him sufficient support to call for the replacement of the Republic’s Chancellor Valorum. Even though the Jedi, the Naboo, and the Gungans were able to repel the invasion, Palpatine succeeded in his goal of having Valorum forced out of office. After being elected to succeed Valorum, Palpatine began consolidating his power and preparing for a galactic conflict that would enable the Sith to supplant the Republic.
Ten years later the Neimoidians allied themselves with the former Jedi Count Dooku, and joined with other hostile species and business interests in forming the Confederacy of Independent Systems. The Neimoidians provided a large amount of military equipment and droids to the war effort.
In 18 BBY the Confederacy was finally defeated after the deaths of both Dooku and General Grievous. While Darth Vader killed the leaders of the Confederacy, Palpatine had the Jedi Order eliminated and declared the formation of the Galactic Empire. The Neimodians were forced to accept being ruled by the Empire.