Simplify the following text for a Grade 10 native English-speaking person.
Original: Angered by the arrest of three miners on a dubious charge , Lalor joined the Ballarat Reform League and became the defacto spokesman following his impromptu incendiary speech to the assembled miners on 30 November 1854 in the absence of the League 's president .
Simplified: Peter Lalor became leader of the Reform League on November 30 1854 and made the miners promise to protect their rights and liberties .