Sonbol by Jared I. Magee

An alien invasion is coming. Humanity was given five years to prepare.

Robert "Mack" McAlister, an overachieving young man from Tennessee, wants something more out of life, so he is off to train at the newly formed Global Confederation's Academy Prime in Dublin.

With two full years of the allotted five spent in rallying the planet, McAlister quickly realizes that preparing for the invasion is only a part of the challenge at hand. He must seek to bond with the three other members of his assigned quad of Primrose 33, fighting to form the relationships that make humanity worth saving before the world comes under attack.