To me, the main conflict in this story is between the various people on the train. They are arguing about how they should think of the war. They are also arguing about who should be saddest and whose situation (in terms of sons going off to war) is the worst.
I think this symbolizes a deeper conflict, though. It is a conflict between the people and society. The characters (they are all just anonymous people who have sons who have been called to fight or who have already been in the war) are showing the conflict between individuals' desires to have their own happiness and society's need to have its citizens fight for it in wars.