What events led up to the speeches of Cleon and Diodotus in the assembly?

The speeches were preceded by the revolt in 428-427 on the island of Lesbos, which was led by the city-state of Mytilene. The contadictory speeches were a response to this battle and dealt direct with the two men's opposing views on capital punishment. The decision of what to do with Mytilene prisoners prompted this debate.