Terry Carr & Ted White 
Invasion from 2500 [EPUB ebook] 

As Jack Eskridge sped through the night toward Chicago, the sky was suddenly lit with a flash of brilliance.Jack stopped the car and ran toward the light. He was greeted by a fantastic sight: a huge, weirdly glowing arch, through which were pouring strange-looking tanks, airships and metallic-clad soldiers carrying sinister weapons.Jack knew he had to get away and warn the country of the invasion. But before he could reach Chicago all the major cities in the United States had been conquered by the aliens.No one knew where they came from or what their evil purpose was. Only one thing was certain – they had to be stopped before the whole of mankind fell under their domination.