19th century

In the 19th century, the war between Mexico and the United States took place due to the latter's commercial, economic, and military expansionism, resulting in Mexico losing more than half of its territory. 

Another significant event in the region was the filibustering invasion led by William Walker, which landed in Ensenada on November 29, 1853. The invaders engaged in theft, looting, and all sorts of atrocities. Walker's intention was to form an independent republic of Mexico named Sonora-Baja California, which would later be annexed to the United States. However, his plans were foiled by the heroic Antonio Meléndrez, who managed to expel them, making the filibusters flee across the border. 

In 1850, a group of Sonoran people had found traces of gold in a valley east of Ensenada. It was not until June 1870 that Ambrosio del Castillo, originally from Hermosillo, Sonora, discovered gold in the San Rafael valley, 48 kilometers east of Ensenada. The gold rush began, with American prospectors crossing the border to seek their fortune. By August, there were more than 400 gamblers searching for the precious metal in the San Rafael valley. By 1875, the town had more than 1500 inhabitants. 

After three years of feverish prosperity, the mines started to decline, leading to the decline of Real del Castillo's importance. The capital of the northern district was moved to Ensenada on May 15, 1882, a date considered as its founding day.

In an effort to develop the arid and sparsely colonized areas of the country, the president decreed a new colonization law on December 15, 1883, allowing foreign capital to enter. As a result, Luis Huller, a German naturalized Mexican, obtained the concession in 1884 to delimit lands in an area that comprised the entire surface of the current state of Baja California. Huller partnered with the American George H. Sisson, but lacking sufficient capital to develop everything they acquired, they managed to interest a group of American investors, forming the International Company of Mexico in March 1885, with its main office in Hartford, Connecticut. 

In Ensenada during those years, there were signs of progress everywhere, including the construction of a dock, an increase in businesses, telephones, telegraphs, hotels, and steamship lines regularly connecting Ensenada with San Diego. The objective was to turn Ensenada into a futuristic city and sell land at high prices.

By a decree issued by the Congress of the Union on December 14, 1887, the administration of the peninsula was divided into two districts, the northern district with Ensenada as its capital and the Southern District with La Paz as its capital. However, the prosperity of the American company did not last long due to mismanagement, large debts, and disorganization in some aspects. Additionally, the government of Don Porfirio Díaz faced pressure to keep foreigners out of Ensenada, and they were informed that they should close their offices. In response to this situation, the American company sold its extensive territories, businesses, and rights to a British company.

20th Century and the Modern Era

In 1915, Ensenada ceased to be the municipal seat of the northern district, which was relocated to Mexicali on the orders of Colonel Esteban Cantú.

The British company was intervened and its concession canceled on April 17, 1917, by the government of Don Venustiano Carranza, due to the company's failure to fulfill the agreements made with the government of Don Porfirio Díaz.

In 1930, the Northern and Southern districts of Baja California changed to territories, and the Northern Territory was constituted by three delegations: Mexicali, Tijuana, and Ensenada.

On January 16, 1952, the presidential decree was published, elevating Baja California from a territory to the 29th state of the Mexican Republic, comprising 4 municipalities: Mexicali, Tecate, Tijuana, and Ensenada.