Orphan's destiny - Robert Buettner

The Battle of Ganymede taught Jason Wander about the devastation of war. After seeing the deaths of his troops, as well as his lover, the battle-scarred soldier is ready for peace.
At 25, General Jason Wander has fought and won man's only alien conflict. Now, after long years in space, he's coming home...but to what? Earth's desperate nations, impoverished by war damage and military spending, are slashing defense budgets. There's just one problem with this new worldwide policy-the first alien invasion was merely Plan A.
Suddenly, the real assault begins: Earth is attacked by a vast armada of city-sized warships. To block their invasion, mankind has only one surviving craft and a single guerrilla strike force...a suicide squad led by Jason Wander.