Complex sentence: A mass of "montoneras", armed with torches ran into the square and the Chileans practically exhausted their ammunition trying to contain this new attack, but the Peruvians managed to set the church ceiling on fire.
Split into simpler sentences: A mass of "montoneras", armed with torches ran into the square, and the Chileans practically exhausted their ammunition trying to contain this new attack. Anyway, the Peruvians managed to set the church ceiling on fire.