John C. McLoughlin’s 1987 Toolmaker Koan is a stand-alone science fiction novel.
Only a few million people died during the One-Day War and the Disturbance that followed. To preclude further hostilities, the overcrowded, poisoned Earth was divided between the Greater Columbian Alliance (essentially North and South America) and the United People’s Democratic Republics of Africa and Eurasia (everyone else). Both sides are mutually hostile, vigilant, and heavily armed — but peace is ensured. The alternative, after all, is total species extinction.
Far out towards the Oort Cloud, a Democratic Republics’ space probe discovers a curious object. A third party has entered the game. This new faction is alien.