Final answer:
Commodore George Dewey's attack on the Spanish fleet at Manila Bay was motivated by the desire to establish naval bases in the Pacific and expand American markets into China.
Step-by-step explanation:
The motive behind Commodore George Dewey's attack on the Spanish fleet at Manila Bay was to further the American military strategists' vision of establishing naval bases in the Pacific Ocean and expanding American markets into China. The attack was a part of the larger strategy to acquire territories and establish the United States as a global power. By sinking the Spanish fleet and capturing the Philippines, the United States achieved a significant military victory and set the stage for the subsequent colonization of the islands.