which factor greatly contributed to the failure of the roman republic? the parthians formed an alliance with the greek city states to defeat the romans. as more and more people would move to the colonies, the urban population declined. the administration could no longer sustain the ever expanding empire, leaving remote provinces without governors. as the elite grew more wealthy, they would buy up all the land from the small farmers who were engaged as soldiers in the foreign wars, thus depleting the agricultural backbone of the republic.