The United States Congress is the legislature of the federal government of the United States. It is bicameral, composed of a lower body, the House of Representatives, and an upper body, the Senate. It meets in the United States Capitol in Washington, D.C. Senators and representatives are chosen through direct election, though vacancies in the Senate may be filled by a governor's appointment. Congress has 535 voting members: 100 senators and 435 representatives. The vice president of the United States has a vote in the Senate only when senators are evenly divided. The House of Representatives has six non-voting members.The sitting of a Congress is for a two-year term, at present, beginning every other January. Elections are held every even-numbered year on Election Day. The members of the House of Representatives are elected for the two-year term of a Congress. The Reapportionment Act of 1929 establishes that there be 435 Representatives and the Uniform Congressional Redistricting Act requires that they be elected from single-member constituencies or districts. It is also required that the Congressional districts be apportioned among states by population every ten years using the United States Census results, provided that each state has at least one Congressional representative. Each senator is elected at-large in their state for a six-year term, with terms staggered, so every two years approximately one-third of the Senate is up for election. Each state, regardless of population or size, has two senators, so currently, there are 100 senators for the 50 states.

Article One of the United States Constitution requires that members of Congress must be at least 25 years old (House) or at least 30 years old (Senate), have been a citizen of the United States for seven (House) or nine (Senate) years, and be an inhabitant of the state which they represent. Members in both chambers may stand for re-election an unlimited number of times.

The Congress was created by the Constitution of the United States and first met in 1789, replacing in its legislative function the Congress of the Confederation. Although not legally mandated, in practice since the 19th century, Congress members are typically affiliated with one of the two major parties, the Democratic Party or the Republican Party, and only rarely with a third party or independents affiliated with no party. In the case of the latter, the lack of affiliation with a political party does not mean that such members are unable to caucus with members of the political parties. Members can also switch parties at any time, although this is quite uncommon.

The Republic of Texas (Spanish: República de Tejas) was a sovereign state in North America that existed from March 2, 1836, to February 19, 1846, although Mexico considered it a rebellious province during its entire existence despite the Treaties of Velasco. 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 Anglo residents of the republic were known as Texians.

The region of the Mexican state of Coahuila y Tejas, now commonly referred to as Mexican Texas, declared its independence from Mexico during the Texas Revolution in 1835–1836, when the Centralist Republic of Mexico abolished autonomy from states of the Mexican federal republic. The major fighting in the Texas war of independence ended on April 21, 1836, but the Mexican Congress refused to recognize the independence of the Republic of Texas, since the agreement was signed by Mexican President General Antonio López de Santa Anna under duress as prisoner of the Texians. There were intermittent conflicts between Mexico and Texas 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 General Santa Anna, who had been captured in battle. The eastern boundary had been defined by the Adams–Onís Treaty of 1819 between the United States and Spain, which recognized the Sabine River as the eastern boundary of Spanish Texas and western boundary of the Missouri Territory. Under the 1819 Adams–Onís Treaty, before Mexico's 1821 independence, 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, since Mexico disputed the independence of Texas. 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. However, the United States inherited the southern and western border dispute with Mexico, which had refused to recognize Texas's independence or U.S. offers to purchase the territory. Consequently, the annexation triggered the Mexican–American War (1846–1848).