War on Pangea

In a parallel reality, Earth still has only one continent - Pangea. When humans evolve onto Earth, they all live on this continent together, without enough space and without enough resources for everyone. This leads to war between the eastern and western halves of Pangea. Now all seventeen-year-olds must join the army and serve for a minimum of three years... if they survive that long. This is the first book in the series.