How did plebeians gain power in the republic? for what changes were they responsible

Rome was divided into two classes.  The patricians or nobility were one class and the plebeians or commoners were the others.  The patricians initially had all the privileges and one of the most important was they can hold office.  The plebeians resented this and rose in revolt.  As a result, reforms were made and eventually the plebeians were given rights as well.

it was displayed because they had a love for war

it granted civil rights to african americans.