What evidence suggests that more than anything else the United States

What evidence suggests that more than anything else the United States went to war with Mexico in order to get possession of California?

What will be an ideal response?

ANSWER
Consider: Polk secretly ordered the navy to seize California in the event of war; Slidell was instructed to buy California; there were rumors that Britain was going to make California a protectorate; Polk instructed the United States consul in California to encourage Californians to agitate for annexation to the United States; Lt. Gillespie was sent to California to foment rebellion against Mexico; General Kearny was dispatched to seize New Mexico and California the moment war began; Polk accepted the terms of the Treaty of Guadalupe Hidalgo which ceded California to the United States