Complex sentence: Unlike in 1798, the preparations for the uprising were successfully concealed, but a premature explosion at one of Emmet's arms depots killed a man and forced Emmet to bring forward the date of the rising before the authorities' suspicions were aroused.
Split into simpler sentences: Unlike in 1798, the revolutionaries concealed their preparations, but a premature explosion at one of Emmet's arms depots killed a man. Emmet was forced to advance the date of the rising before the authorities' suspicions were aroused.