Mexico-United States border in the context of "List of Mexico–United States border crossings"

Arizona is a landlocked state in the Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the northwest and California to the west, and shares an international border with the Mexican states of Sonora and Baja California to the south and southwest. Its capital and largest city is Phoenix, which is the most populous state capital and fifth-most populous city in the United States. Arizona is divided into 15 counties.

Arizona is the sixth-largest state by area and the 14th-most-populous of the 50 states. It is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912. Historically part of the territory of Alta California and Nuevo México in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848, where the area became part of the New Mexico Territory. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.

New Mexico is a landlocked state in the Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also borders the state of Texas to the east and southeast, Oklahoma to the northeast, and shares an international border with the Mexican states of Chihuahua and Sonora to the south. New Mexico's largest city is Albuquerque, and its state capital is Santa Fe, the oldest state capital in the U.S.—founded in 1610 as the government seat of Nuevo México in New Spain—and the highest in elevation, at 6,998 feet (2,133 m).

New Mexico is the fifth-largest of the fifty states by area, but with just over 2.1 million residents, ranks 36th in population and 45th in population density. Its climate and geography are highly varied, ranging from forested mountains to sparse deserts; the northern and eastern regions exhibit a colder alpine climate, while the west and south are warmer and more arid. The Rio Grande and its fertile valley runs from north-to-south, creating a riparian biome through the center of the state that supports a bosque habitat and distinct Albuquerque Basin climate. One–third of New Mexico's land is federally owned, including many protected wilderness areas, 15 national parks and monuments, and three UNESCO World Heritage Sites wholly contained within the state—the most of any U.S. state.

San Diego County (/ˌsæn diˈeɪɡoʊ/ ), officially the County of San Diego, is a county in the southwest corner of the U.S. state of California, north to its border with Mexico. As of the 2020 census, the population was 3,298,634; it is the second-most populous county in California and the fifth-most populous in the United States. Its county seat is San Diego, the second-most populous city in California and the eighth-most populous in the United States. It is the southwesternmost county in the 48 contiguous United States, and is a border county. It is home to 18 Indian reservations, the most of any county in the United States. There are 16 military installations of the U.S. Navy, Marine Corps, and Coast Guard in the county.

San Diego County comprises the San Diego–Chula Vista–Carlsbad, CA Metropolitan Statistical Area, which is the 18th most populous metropolitan statistical area and the 18th most populous primary statistical area in the United States. San Diego County is also part of the San Diego–Tijuana region, the largest metropolitan area shared between the United States and Mexico. From north to south, San Diego County extends from the southern borders of Orange and Riverside counties to the Mexico–U.S. border and the municipalities of Tijuana and Tecate in Baja California. From west to east, San Diego County stretches from the Pacific Ocean to its boundary with Imperial County, which separated from it in 1907.

The Mexico–United States border crisis is an ongoing migrant crisis in North America concerning the illegal migration of people into the United States across the Mexico-United States border. U.S. presidents Barack Obama and Donald Trump both referred to surges in migrants at the border as a "crisis" during their tenure. Following a decline in migrants crossing the border during the first Trump administration, illegal border crossings surged during the Biden administration, with over 7.2 million migrants encountered between January 2021 and January 2024, not counting gotaways. Experts have attributed the increase in attempted crossings to pent-up demand, changes in global migration patterns, a change of perceptions by migrants about the ease of crossing, and incentives for migrants to try to cross again after Title 42 expulsions. The number of migrants sent back increased as a result, though the percentage sent back decreased. Border apprehensions fell back to 2020 levels in mid-2024.

The migrants, who are mostly of Guatemalan, Salvadoran, Honduran, and Venezuelan citizenship, are reported to be escaping economic hardship, gang violence and environmental disaster in their home countries (particularly acute in Guatemala and Honduras) to seek asylum in the US. Unlike the demographic of migrants in the preceding years, an increasing proportion of current migrants arriving at the Mexico–US border are children, including unaccompanied children and from countries outside Latin America.

Interstate 35 (I-35) is a major north–south Interstate Highway that runs from Laredo, Texas near the Mexican border to Duluth, Minnesota. In Texas, the highway begins in Laredo and runs north to the Red River north of Gainesville, where it crosses into Oklahoma. Along its route, it passes through the cities of San Antonio, Austin, and Waco before splitting into two branch routes just north of Hillsboro: I-35E heads northeast through Dallas, while I-35W turns northwest to run through Fort Worth. The two branches rejoin in Denton to again form I-35, which continues to the Oklahoma state line. The exit numbers for I-35E maintain the sequence of exit numbers from the southern segment of I-35, and the northern segment of I-35 follows on from the sequence of exit numbers from I-35E. I-35W maintains its own sequence of exit numbers.

In Texas, I-35 runs for just over 503 miles (810 km), which does not include the 85-mile (137 km) segment of I-35W. It does include the 97-mile (156 km) segment of I-35E. Texas contains more miles of the overall length of I-35 than any other state, almost one-third of the entire length.