Kumeyaay warriors were learning better warfare techniques and vulnerabilities from Missionized Kumeyaay ("Diegueno"), who decided to return to the free territories.
In 1823, Captain Jose Romero tried to reestablish the overland route to Sonora. He arranged a meeting with the Quechan to negotiate an agreement to allow travel through their territory. At first the Quechan seemed agreeable, but while crossing the river they took all of the Captain's supplies and horses, leaving them barely enough to make a difficult journey back tot he Mission lands.
In 1825, Kumeyaay attacked visiting American Captain Benjamin Morrell, while on a hunting expedition, inland from San Diego - the first record of an American being attacked by Kumeyaay.
Lt. Juan M. Ibarra led several attacks into Kumeyaay territory, in retaliation for Kumeyaay raids. In April of 1826, he struck Santa Ysabel, killing 28 people. He then led his force of Mexcians and Converted Indians against the Kumeyaay of San Felipe Valley, killing more before returning.
By 1836, the Quechan controlled overland access to Sonora, and Kumeyaay raids had forced the abandonment of inland ranches. Residents gathered in San Diego and threatened the Mexican officials with abandoning the city if they could not be protected. Attempts at driving the Kumeyaay from the mountains were unsuccessful. The Kumeyaay maintained control from the Cuyamaca Mountains, east.
A large force of Kumeyaay gathered to launch an attack on the City of San Diego. They were forced to retreat when naval guns from the ship "Alert" fired on the warriors.
July, 1837 - Rancho San Bernardo was attacked, killing three people.
In 1840, Sir Edward Belcher - on Her Majesty's Ship Sulfur put into the port at San Diego. Noting the condition of the city, he noted that it appeared that San Diego would soon be taken by the Indians, or by another nation (due to its weakened condition.
All of the ranchos were abandoned, or rendered unusable by 1844. Kumeyaay were launching raids deep into Mexican coastal territory.
May, 13, 1846, war was declared on Mexico by the United States of America.