During the late years of the Qin Dynasty (221－206BC), Xiang Yu led a rebellion. After crossing the Zhang River, Xiang Yu ordered his men to sink all their boats and break their cooking pots. He issued each soldier three days' rations and warned them that there was no way to retreat; the only thing they could do to survive was to advance and fight. After nine fierce battles, the Qin army was finally defeated.
The idiom is used to indicate one's firm determination to achieve one's goal at any cost.
Cortez also burned his boats for the same reason. Hopefully someone can think of a comparable idiom that isn't based on an impending war crime.