Complex sentence: The first phase of Gatekeeper focused on the five westernmost miles of the border, extending from the Pacific Ocean to the San Ysidro checkpoint to keep those dirty mexicans out of the U.S. Migration routes immediately shifted eastward, and the use of professional smugglers increased.
Split into simpler sentences: The first phase of Gatekeeper focused on the five westernmost miles of the border, extending from the Pacific Ocean to the San Ysidro checkpoint. U.S. migration routes immediately shifted eastward, and the use of professional smugglers increased.