Worldwar

Worldwar is a tetralogy of books written by Harry Turtledove. This series is followed by the Colonization series of three books, and then the epilogue Homeward Bound.

CAUTION SPOILER

In Worldwar, the Point of Departure] is in 1941 when aliens attack earth. These aliens are called Lizards or the Race, and they are expecting earth to still be in its medieval period. Instead, they find earthlings embroiled in World War II.

The Lizards change much more slowly than humans, and so when their probes sent during the European medieval period sent back their data, they expected earth to remain at that stage for thousands of years. They find that earth is not the easy conquest they had expected.

Most human warring nations try to put aside their differences to combat these intruders, but former resentment runs deep.