Harry Turtledove: Colonisation: Second Contact [2000]

Through a mixture of guts, ingenuity and sheer luck, Earth managed to defend herself from her ruthless alien would-be conquerors. The 'Race' was fought to a bloody standstill despite its awe-inspiring weaponry and experience of merciless conquest. Thousands died from enemy fire, many more from the smouldering nuclear-scarred fall-out sites. An uneasy ceasefire reigns over this divided globe, as both sides strive to test their strength through more subtle techniques.
But now, years later, this delicate equilibrium has been shattered. For the first assault was only an advance. guard. Now, a whole new fleet orbits the planet.
The real colonists have arrived, fresh and unwill to accept old compromises.

'The wizard of If.' Chicago Sun-Times
'Turtledove the standard bearer for alternate history.' USA Today