The irony of lived time
To the people who existed throughout history, they didn't have the opinion that modern students have about them. They weren't walking around saying, "It's a nice day in the past!" That's the first irony of this novel, that to the people in the past, it was just the present. That is an irony about time that is hard to conceive of, especially if one is asked to learn about epic swathes of time, memorizing names and facts—it can be hard to remember that history really happened.
The irony of loyalties
To the kids, one of the most troubling dilemmas is that they don't know whose side to pick. This is a demonstration of their competitive understanding of history, because they want to pick the side they align most with, but there is no picking sides in a war one does not understand. They realize that beyond their interests in picking a side, they now have to worry about survival. They don't want to pick the side whose ideas are most like their own. They want to survive the war that is coming.
The stakes of war
The trio are forced to re-learn what warfare is. They realize that war doesn't have the same meaning as it did back in the classroom. In the classroom, war is a fact to be memorized. They learn statistics about death tolls so they can get the answer right. But, now they're trapped on the cusp of real war, and they suddenly realize that their deaths would only mean three more deaths on the death toll, and suddenly, they have a more serious appreciation for the loss of human life in death. They realize how many people have died in wars throughout history, and finally, the horror and tragedy of that sets in a little deeper.
The boredom with history
Certainly, the central characters are no longer bored by history. They have to learn rapidly in order to survive, because history is so much different than they expected. In fact, the ways that culture can change through time are downright disturbing to them at some points, even sublime. This is ironic, because as students, they often became bored by history, either because of the presentation or because of the setting, but now that they're living it, it is different.
Empathy for the past
Dak, Sera, and Riq all realize something they never considered. When they are spending time in these ancient communities, they make friends and depend on ancient people. This is ironic, because it means that the people from the past are just like them—people. The trio learns that they are able to empathize with the people of the past just as they have learned to empathize with people from different parts of the world.
