To appeal to his audience, in “war message to congress,” wilson mostly relies on

I believe the answer is: pathos, an appeal based on emotions.

In war message to the Congress, Wilson appeal to the audience emoiton by maintaining the sacrifice that American citizens have suffered in order to influence congress to declare a war against Germany.

It could be seen from this sentence:

American ships have been sunk, American lives taken, in ways which it has stirred us very deeply to learn of