Why did the plebeians eventually gain a larger role in the roman republic

The Plebians revolted until a tribune was created in which they could elect their own representatives. The struggle of the orders was a fight for political equality with the patricians. While Rome was at war, all of the Plebeians left the city secession and created the office of the Plebeian Tribune. see Wiki answer.

The Plebeians revolted until a tribune was created in which they were able to elect their own reps. The struggle of the Orders was a fight for political equality with the Patricians. In the process when Rome was at war, all of the Plebeians left the city in secession and created the office of the Plebeian Tribune. This established the first real power of the Plebeian ever had. They wanted full power in the Senate, but a small a small group of Patricio-Plebeian aristocrats continued to hold the means to control the Plebeian council. 

Spanish conquistadors demanded labour from natives.