Complex sentence: In 1848 California officially became a part of the United States of America, following several years of battles in the Salinas area with John Fremont flying the American flag on the highest peak of the Gabilan Mountains and claiming California for the United States.
Split into simpler sentences: In 1848 California officially became a part of the United States of America. This transition followed several years of battles in the Salinas area with John Fremont flying the American flag on the highest peak of the Gabilan Mountains and claiming California for the United States.