How does Julius Caesar's ambition prove to be his downfall? Why does Julius Caesar refuse the crown while he desperately wants it?

While Caesar seemed to truly have Rome's best interest at heart, his personal ambition was seen as a threat by the conspirators. Ancient Rome began as a monarchy in 753 BCE with one king in charge. In 509 BCE, the last of the kings, Tarquin the Proud, was deposed and Rome became a republic. As such, the citizens had a voice through their representatives. Had Caesar taken the crown when he was offered it in 44 BCE, Rome would have returned to a monarchy or become a dictatorship. The conspirators feared this and so they assassinated him. Ironically, in 27 BCE Caesar's adopted nephew, Octavian Augustus, assumed the throne as emperor. Rome was ruled by one person until its fall in 476 CE.

Ironically, despite being accused of being too ambitious, in his will Caesar left money to the Roman people and all of his property to be turned into parks for the Roman citizens.