Isolated by an ocean, deserts, forests and mountains surrounding it on many sides and far away from the European mainland, colonization of California came slowly and late. The first Europeans to claim dominion over the land were the Spanish, who slowly established mission towns and ranches. After the Mexican Revolution against Spanish rule, California fell under the rule of Mexico in 1821, but continued to be ignored due to constant internal strife within the Mexican government. The nineteenth century saw the United States expanding ever westward and in June 1846 the Mexican-American War began. When American settlers of Sonoma, California, heard about the fighting, they began a revolt which was eventually aided by the U.S. Navy, Marines and a group of mountain men. The war ended in 1847 and established the US-Mexico border at it's current boundaries.