Mandate of Heaven refers to the belief that whoever become the rulers in China obtain the position because the Gods intended them to. So, they believe that if one ruler is killed and changed by another rulers, it happened because the initial ruler is deemed as 'unworthy' by the heaven to continue his reign.
Many people in Tang & song dynasties justify the cruel things that they did through this belief. The see that the word of the emperor is the word from the heaven that must be obeyed by all citizens.
A bartering system relies too much on being paid back/loyalty between 2 or more people. Money is more reliable as it allows for wealth to be distributed
Khrushchev's 24 October 1962 letter rejected Kennedy's “ultimatum” and declared that the quarantine was an illegal and “piratical act” derived from the President's “hatred for the Cuban people.”