It starts with the Mexican American War.
The Mexican-American War
The Spaniards had long feared that other European powers were planning to invade their sparsely populated northern frontier. They sparred with the French and English in the Mississippi Valley and watched the Russians expand down the Pacific coast, but after Mexico won its independence from Spain, it was the growth of the United States that proved most significant. The process began with Texas in 1836. Six years later, Mexico's secretary of state, Lucás Alamán, warned, "Where others send invading armies...[the Americans] send their colonists." Desperate to fill empty spaces, Mexico invited Americans and other foreign colonists to settle in Texas in 1824. By 1830 there were already more than twice as many Anglos as Mexicans there (7,000 to 3,000). By 1836 the ratio had risen ten to one. When Sam Houston led his rebels to victory at San Jacinto, Texas remained an independent republic until 1845. Mexicans of Texas soon became a minority in their native land.
"Mexicans of Texas soon became a minority in their native land." Their native land?? Their native land!! How could it be their 'native land' when the Spanish are the ones which colonized the area?? Prior to, and mostly during the claim of ownership for the territory. The original area belonged to the Native Indigenous and not the Mexicans (with less than 3000 Mexican Nationals in 1821) nor the Spanish (where most of the settlements were between the Nueces River and the Rio Grand River. The Texas Revolution in 1836, was a revolution of Mexican citizens, who revolted against the take over of the Mexican government by a dictator. The flag that flew over the Alamo was a Mexican flag with the year 1824 in the middle of it. The reason it has the date 1824, was that this was the date of the Mexican constitution that had been caste aside by Santa Anna.
During Spanish (1598-1821) and Mexican (1821-1846) rule over what was to become the U.S. Southwest, the governments made land grants to various individuals and communities. Under the Treaty of Guadalupe Hidalgo (1848), which ended the Mexican-American War, the United States obtained these territories, and in Article VIII guaranteed the rights of Mexican and former Mexican citizens to their property. However, the U.S. Senate in ratifying the treaty eliminated Article 10, which stated that the U.S. government would honor and guarantee all land grants awarded in lands ceded to the United States to citizens of Spain and Mexico by those respective governments. Thus land grants were subject to being proved.
In 1851, Congress passed the first legislation implementing the property protection provisions of the Treaty of Guadalupe Hidalgo, however it addressed only the Spanish and Mexican grants in California. Congress focused on California’s land grants first because California was already a populous state, and it wanted to encourage further settlement of the public domain land there.
In 1854 the U.S. Congress established the office of the Surveyor General of New Mexico to ascertain "the origin, nature, character, and extent to all claims to lands under the laws, usages, and customs of Spain and Mexico." At first the Congress tried to deal with each land grant by special bill and the House had a Committee on Private Land Claims, seats on which were sought after as a way of dispensing patronage. By 1880 the corruption inherent in determining these claims by politics rather than on a legal basis forced an end to this practice. For ten years no claims could be proved as against the United States.
So the U.S. Congress, in 1891, created the Court of Private Land Claims consisting of five justices appointed for a term to expire on December 31, 1895. The court itself was to exist only during this period, although its existence and the terms of the justices were from time to time extended until June 30, 1904. This court was given jurisdiction over claims to land in the territories of New Mexico, Arizona, and Utah, and in the states of Nevada, Colorado, and Wyoming, which had not been previously proved and affirmed by the United States. Many of these Spanish or Mexican land grants were based upon incomplete documentation, in part because those governments did not issue deeds to the grantees, and records were kept variously at the territorial, state, vice-royal or imperial level.
Treaty of Guadalupe Hidalgo and the changes made by the US Government.
The version of the treaty ratified by the United States Senate eliminated Article X, which stated that the U.S. government would honor and guarantee all land grants awarded in lands ceded to the United States to citizens of Spain and Mexico by those respective governments. Article VIII guaranteed that Mexicans who remained more than one year in the ceded lands would automatically become full-fledged American citizens (or they could declare their intention of remaining Mexican citizens); however, the Senate modified Article IX, changing the first paragraph and excluding the last two. Among the changes was that Mexican citizens would "be admitted at the proper time (to be judged of by the Congress of the United States)" instead of "admitted as soon as possible", as negotiated between Trist and the Mexican delegation.
The treaty was subsequently ratified by the United States Senate by a vote of 38 to 14 on March 10, 1848 and by the Mexican government by a legislative vote of 51 to 34 and a Mexican Senate vote of 33 to 4, on May 19, 1848.
Protocol of Querétaro
On May 30, 1848, when the two countries exchanged ratifications of the treaty of Guadalupe Hidalgo, they further negotiated a three-article protocol to explain the amendments. The first article stated that the original Article IX of the treaty, although replaced by Article III of the Treaty of Louisiana, would still confer the rights delineated in Article IX. The second article confirmed the legitimacy of land grants pursuant to Mexican law.
The protocol further noted that said explanations had been accepted by the Mexican Minister of Foreign Affairs on behalf of the Mexican Government, and was signed in Querétaro by A. H. Sevier, Nathan Clifford and Luis de la Rosa.
The United States would later go on to ignore the protocol on the grounds that the U.S. representatives had over-reached their authority in agreeing to it.
Treaty of Mesilla
The treaty of Mesilla which concluded the Gadsden purchase of 1854 had significant implications for the treaty of Guadalupe Hidalgo. Article II of the treaty annulled article XI of the treaty of Guadalupe Hidalgo, and article IV further annulled articles VI and VII of Guadalupe Hidalgo. Article V however reaffirmed the property guarantees of Guadalupe Hidalgo, specifically those contained within articles VIII and IX.
On to the technical details.
Before Mexico won its independence from Spain in 1821, the Spanish government had made a few small grants of land in southern Arizona. In 1789, Toribio de Otero petitioned for a lot from the Tubac presidio in return for military service. The land remained in the Otero family until 1938. In 1807, the O'odham of the Tumacacori mission received title to a long strip along the Santa Cruz River south of Tubac encompassing the former mission lands of Tumacacori, Calabasas, and Guevavi. Part of this grant was the land auctioned off in Guaymas in 1846. In 1812, Agustín Ortiz purchased the site of Arivaca, an important mining and ranching center since the mid eighteenth century, at public auction. Charles Poston purchased that hacienda from Ignacio Ortiz in 1856 for $10,000.
However, most grants in Arizona were made after Mexico gained independence. In 1821, Tomás and Ignacio Ortiz received a total of about 17,000 acres (69 km²) of land known as San Ignacio de la Canoa and located between Tubac and modern Sahuarita. The following year, the ranch of San Bernardino east of modern Douglas became the property of Lieutenant Ignacio Pérez. It totaled more than 73,000 acres (300 km²) in Arizona and northeastern Sonora. León Herreros acquired San José de Sanoita in 1825, while "Ramón Romero and other shareholders, their children, heirs, and successors received title to San Rafael de la Zanja in the San Rafael Valley the same year. The Mexican government issued five more grants, including Buenavista, San Rafael del Valle, San Juan de las Boquillas y Nogales, Tres Alamos, and the Babocómari ranch, between 1826 and 1831.
During the 1820s and 1830s, Sonoran ranchers strove to colonize the grasslands of southeastern Arizona. Their legal tool was the land grant and their instrument of occupation was the mixed-breed longhorn cow. These longhorn, or their descendants, roamed the range as feral survivors long after their masters were gone.
Hispanic Arizona was again making an effort to roll back the borders of the Apachería. The land grants established Mexican title to much of the Santa Cruz and San Pedro valleys. They also extended Mexican domain over the plains south of the Chiricahua Mountains. Most of the cattle country ended up in the hands of the Elías-González family or their relatives. During the colonial period, the Spanish government supported the mission and the presidial systems in order to insure royal control over the northern frontier. By the 1820s, however, private capital had become the usual method of colonization, and most of that capital belonged to a network of elite families who dominated northern Sonora at the time. They provided the livestock and took the risks.
If the Elías-Gonzálezes and their neighbors had received the land grant twenty years earlier, when they would have been protected by the presidios and the Apache peace program, they might have succeeded, but beginning in the 1820s, the Apaches began to burn their buildings and kill their cowboys, run off their horses, and slaughter their beef. By 1840 most of the grants had been abandoned. Even though the U.S. Court of Private Land Claims eventually confirmed eight of the Spanish and Mexican land grants in the early twentieth century, none of the descendants of the original grantees managed to hold on to their titles. John Slaughter owned the San Bernardino Ranch north of the U.S.-Mexico border, and Colin Cameron's San Rafael Cattle Company had acquired the San Rafael de la Zanja grant. Largescale ranching did not return to the area until the 1880s after most of the Apaches had been confined to reservations. When it did, American land-and-cattle companies, not the Mexican elite, held them.
The most blatant land grab occurred in 1844. Far to the south, in the port of the Guaymas, the Mexican government declared that the mission lands of Tumacacori had been abandoned and auctioned them off for five hundred pesos to Francisco Alejandro Aguilar. The few Pimas who had not been driven away by Apache depredations neither knew about nor consented to the sale. Aguilar was the brother-in-law of Manuel Mariá Gándara, one of the most powerful military strongmen in Sonora. He turned Calabasas into his own private hacienda, and by the late 1840s Pima dispossession along the Santa Cruz was nearly complete.
Some presidial soldiers became so poor that they had to sell their weapons to feed their families. In 1840 and 1841 the Mexican government campaigned against the Tohono O'odham of the western deserts, their former allies. The colony reached its nadir at midcentury. In 1843 the Apaches killed at least thirty shareholders of the San Rafael de la Zanja grant at La Boca de Noria near modern Lochiel. Ranching ceased in the San Rafael Valley. Five years later, at least fifteen Tucsonenses, including nine presidial soldiers, rode into ambush in the Whetstone Mountains. By the time the bodies could be recovered, they were so decomposed that the remains had to be carried back to the presidio of Santa Cruz in sacks. Tubac itself was abandoned once again after an Apache assault in January 1849.