The Fithp an alien race that resemble baby elephants have come to Earth to conquer. They are a herd mentality species. In their world when two herds meet they fight one another until the one surrenders. Then the losing herd is incorporated into the winning herd. The Fithp seem confused when humans attempt to initiate peaceful contact first. Also the humans seem to not know how to properly surrender.
The initial acts of the Fithp is to destroy the space station in orbit then bomb all the bridges, dams and roads on the planet. They then follow with an invasion of Kansas demanding complete submission. The U.S. and Soviets respond with a nuclear attack on Kansas to drive them off. The Fithp retaliate by dropping a large asteroid into the Indian ocean killing millions. A successful invasion of Africa follows.
The only chance for the humans is to build a ship powered by nuclear explosions to take on the mother ship in orbit.
The cover says that this is probably the finest novel of alien invasion ever written and I agree. I received the hardcover edition as a Christmas present back in 1985. It made me a fan of Niven and Pournelle. I have since read many of their books. This is probably my favorite.
What I like is that the aliens are truly alien. They have a completely different physical and psychological makeup yet each character has his own emotions and personality. The cast of characters both alien and human is diverse. The technology sounds realistic and plausible. The Orion ship powered by nuclear explosions is actually a real concept.
So if you like epic alien invasion stories than this is a must have for your library.