How is The Lord of the Flies an extended metaphor?
LOTF is metaphored to the world in general. Keep in mind that Golding wrote this novel after his experiences fighting in WWII. The destruction of a beautiful island by this group of boys is paralleled to the destruction of Europe by various armies. On this island, we have a group of people with an opportunity to work together and make a great society while attempting survival. Instead, the hunger for power drives them into separate tribes and begin a mini-war on the island. Now, relate that to what you know about Europe in both world wars. There were some great opportunites for great leaders to work together to build a great continent of trade and economy. Instead, the power driven few attempted violent takeover.
While this novel can be viewed as a broad generalization of a post-war Europe, the elements of irony with-in the text are more specific examples of that extended metaphor. Note how the naval officer at the end seems to condemn the behavior of the boys on this island while he watches in full military uniform with his war craft in the background. Many of the leaders of various nations seemed to condemn the behavior of other countries leaders during the world wars, yet that didn't stop these leaders from engaging in the same activities with their own nations.