Alea iacta est

From Infogalactic:

Alea iacta est ("The die is cast") is a Latin phrase attributed by Suetonius to Julius Caesar on January 10, 49 BC as he led his army across the River Rubicon in Northern Italy. With this step, he entered Italy at the head of his army in defiance of the Senate and began his long civil war against Pompey and the Optimates.

A civil war that Caesar won although he was assassinated shortly after becoming "dictator in perpetuity" of the Roman Empire.