Several Spanish expeditions contributed to the early exploration of Texas, beginning in 1519. In 1528, an expedition was shipwrecked on the Texas coast. After wandering for eight years among the Indians, the group returned to Mexico with stories of cities of great wealth that they had supposedly seen. Expeditions were sent out repeatedly in the next few years, but gold was never found. French explorers visited Texas in the 1680s, and La Salle claimed much of Texas as part of his huge claim of land for France. The French attempted to establish a colony, but when the Spanish sent an expedition to destroy it, they found only abandoned ruins. The territory remained firmly under Spanish control through the 18th century, but when the United States made the Louisiana Purchase in 1803, it put forward claims of its own, based on earlier French claims. However, the border issue was resolved through treaty. Growing numbers of American settlers, who were at first welcomed, began to concern Mexico. When Mexico closed Texas to further American immigration, tensions rose. Independence was declared and after a war that saw defeat at the Alamo and victory at the Battle of San Jacinto, Texas emerged as a Republic. Although Texans would have readily joined the United States, pressures from various sources kept them out until 1845. After the Mexican war of 1846 to 1848, Mexico gave up all claims to Texas. Although Texas joined the Confederacy during the Civil War, there was considerable pro-Union sentiment in the state. Governor Sam Houston refused to support the Confederacy and was removed from office. The final battle of the Civil War was fought near the mouth of the Rio Grande by soldiers who were unaware that the war had ended a month earlier. During the Reconstruction of Texas, a legal controversy arose regarding the legal nature of the Texas secession. It was known as the Ab-Initio Movement. According to its supporters, the secession of Texas from the Union had been null and void from the very beginning, and consequently all laws derived from the secession and all public and private relations based on those laws were in turn null and void. The majority view rejected this extreme position, and the Republicans, the party of Reconstruction, were deeply divided for a period of three years. The Ab-Initios were led by Morgan Hamilton and the Anti-Ab-Initios by his brother, former governor A.J. Hamilton. In the end, the latter group prevailed, albeit with certain compromises. Texas continued to grow rapidly. In the 1870s, cattle from Texas was driven to market along trails to Missouri and Kansas. Starting with the discovery of the Spindletop oil field in 1901, Texas` petroleum and natural gas industries grew to be the largest in the United States. Texas, in common with other Southern states, attempted to restrict the voting rights of blacks despite the provisions of Amendment XV giving them suffrage. One technique was to disallow them from participating in primary elections, on the theory that this was a private affair of the party. Texas enacted a statute in 1923 which stated that, "in no event shall a Negro be eligible to participate in a Democratic Party primary election held in the state of Texas." In the one-party South, the Democratic primary was tantamount to the general election, so this rule effectively disenfranchised blacks in Texas. In 1927, the Supreme Court ruled in the case of Nixon v. Herndon, with Oliver Wendell Holmes writing the opinion, that the Texas law violated the Fifteenth Amendment.