U.S. auto sales rose 11% in December, capping a year that suggests the industry is on the verge of one of the most dramatic shifts in its history.

For most of the past century, the U.S. car industry was dominated by General Motors Co., Ford Motor Co. and Chrysler Group LLC. Now, as a result of both long-term trends and the upheaval of the last two years, the Big Three are about to be replaced by a Gang of Seven as the industry's driving force.

In...