What is the benefit of waiting until almost the end of the speech to ask Congress to declare a state of war?

The benefit of waiting to the end of the speech to ask the congress to declare a state of war was as a result of his need to enumerate all points which would point favourably towards the declaration of the war.

He knew that, making his request directly might likely led to being turned down while putting his reasons bare during the speech would grant him more grounds on why the war is a necessity.

Explanation:

these civilizations were located around fertile rivers, where they could produce an abundance of crops