Complex sentence: Even though Darius did not have the support of the populace, Darius had a loyal army, led by close confidants and nobles (including the six nobles with whom he removed Gaumata) with whom he was able to suppress and quell all revolts within a year.
Split into simpler sentences: Even though Darius did not seem to have the support of the populace, Darius had a loyal army, led by close confidants and nobles (including the six nobles who had helped him remove Gaumata). With their support, Darius was able to suppress and quell all revolts within a year.