In 1845, Frémont started on his third trip, this time entering California by a southern route and finding himself at Sutter's early in 1846. In some respects his detachment of engineers had the appearance of a filibustering party from the start. When it crossed the Rockies, it began to trespass upon the territory belonging to Mexico, with whom the United States was yet at peace. Whether the explorer was actually instructed to detach California from Mexico, or whether he only imagined that such action would be approved at home, is likely never to be explained. Naval officers on the Pacific were already under orders in the event of war to seize California at once; and Polk was from the start ambitious to round out the American territory on the Southwest. The Americans in the Sacramento were at variance with their Mexican neighbors, who resented the steady influx of foreign blood. Between 1842 and 1846 their numbers had rapidly increased. And in June, 1846, certain of them, professing to believe that they were to be attacked, seized the Mexican village of Sonoma and broke out the colors of what they called their Bear Flag Republic. Frémont, near at hand, countenanced and supported their act, if he did not suggest it. The news of actual war reached the Pacific shortly after the American population in California had begun its little revolution. Frémont was in his glory for a time as the responsible head of American power in the province. Naval commanders under their own orders coöperated along the coast so effectively that Kearny, with his army of the West, learned that the conquest was substantially complete, soon after he left Santa Fé, and was able to send most of his own force back. California fell into American hands almost without a struggle, leaving the invaders in possession early in 1847. In January of that year the little village of Yerba Buena was rebaptized San Francisco, while the American occupants began the sale of lots along the water front and the construction of a great seaport.