Complex sentence: An imperial emissary from Emperor Xian was sent to broker peace, but was turned down, then Ma Teng's close friend and comrade, Han Sui was sent to dissuade the rebel with an armed force.
Split into simpler sentences: An imperial emissary from Emperor Xian was sent to broker peace, but to no avail. Then, Ma Teng's close friend and comrade, Han Sui, was sent to dissuade the rebel with an armed force.