Which of the following did Mexico and the Republic of Texas continue to fight about in the 1840s?

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Explanation:

The Republic of Texas (Spanish: República de Tejas) was a sovereign nation in North America that existed from October 2, 1835, to February 19, 1846. It was bordered by Mexico to the west and southwest, the Gulf of Mexico to the southeast, the two U.S. states of Louisiana and Arkansas to the east and northeast, and United States territories encompassing parts of the current U.S. states of Oklahoma, Kansas, Colorado, Wyoming, and New Mexico to the north and west. The citizens of the republic were known as Texians.

The region of the Mexican state of Coahuila y Tejas commonly referred to as Mexican Texas declared its independence from Mexico during the Texas Revolution in 1835–1836. The Texas war of independence ended on April 21, 1836, but Mexico refused to recognize the independence of the Republic of Texas, and intermittent conflicts between the two states continued into the 1840s. The United States recognized the Republic of Texas in March 1837 but declined to annex the territory.The Republic-claimed borders were based upon the Treaties of Velasco between the newly created Texas Republic and Antonio López de Santa Anna of Mexico. The eastern boundary had been defined by the Adams–Onís Treaty of 1819 between the United States and Spain, which recognised the Sabine River as the eastern boundary of Spanish Texas and western boundary of the Missouri Territory. Under the Adams–Onís Treaty of 1819 the United States had renounced its claim to Spanish land to the east of the Rocky Mountains and to the north of the Rio Grande, which it claimed to have acquired as part of the Louisiana Purchase of 1803.

The republic's southern and western boundary with Mexico was disputed throughout the republic's existence. Texas claimed the Rio Grande as its southern boundary, while Mexico insisted that the Nueces River was the boundary. In practice, much of the disputed territory was occupied by the Comanche and outside the control of either state, but Texian claims included the eastern portions of New Mexico, which was administered by Mexico throughout this period.

Texas was annexed by the United States on December 29, 1845 and was admitted to the Union as the 28th state on that day, with the transfer of power from the Republic to the new state of Texas formally taking place on February 19, 1846.[6] However, the United States inherited the southern and western border dispute with Mexico, which became a trigger for the Mexican–American War (1846–1848).