The international border between Mexico and the United States runs from San Diego, California, and Tijuana, Baja California, in the west to Matamoros, Tamaulipas, and Brownsville, Texas, in the east. It traverses a variety of terrains, ranging from major urban areas to inhospitable deserts. From the border crossing at El Paso, Texas, and Ciudad Juárez, Chihuahua, to the east, it follows the course of the Rio Grande (Río Bravo del Norte) to the Gulf of Mexico; from the same binational conurbation westward to the Pacific Ocean, it crosses vast tracts of the Sonoran and Chihuahuan Deserts, the Colorado River Delta, and the northernmost tip of the Baja California Peninsula.
The border's total length is 1,951 miles (3,141 km), according to figures given by the IBWC.[1] It is the most frequently crossed international border in the world, with some 350 million people crossing legally from one country to the other every year.[2]

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The U.S.–Mexico border has the highest number of both legal and illegal crossings of any land border in the world. Besides the closeness of the two countries, differences in living standards on the two sides of border is the primary driving force behind these migratory flows. The U.S. Border Patrol is too underfinanced and understaffed to effectively fight illegal immigration (with an average of four agents per mile of the border), and the Mexican government, receiving tens of billons of dollars each year in expatriate remittances, stops one step short from actually encouraging emigration. [3] As a result, a large percentage of the border is left virtually unguarded, except by a small number of patrolling agents of the U.S. federal government.

For a period of time in the 1990s U.S. Army personnel were stationed along the U.S.-Mexico border to help stem the flow of illegal aliens and drug smugglers. These soldiers patrolled the border in camouflage uniforms with assault rifles, and assisted the border patrol with their tasks. This eventually led to confrontations between citizens attempting to cross the border who were discovered by soldiers. Eventually, public opinion turned against the use of U.S. Army personnel to secure the border, and this tactic was abandoned. After the September 11, 2001 attacks the United States looked at the feasability of placing soldiers along the U.S.-Mexico border as a safety measure, but nothing along these lines has materialized. It is possible that such a plan is still in the works, or it may have been abandoned in favor of training more Border Patrol Agents. Note that each state in the United States has a National Guard garrison that could be placed on the border at a state’s discretion to assist with border security; many states also have a State Defense Force that could also be activated for this purpose. However, no state has ever exercised such an option.

It is estimated that over a million people cross the border illegally each year, most of whom are of Mexican origin. The rest are labeled "Other Than Mexicans" (OTM), of whom a majority are Central Americans. Border Patrol activity is concentrated around big border cities such as San Diego and El Paso. This means that the flow of illegal immigrants is diverted into rural mountainous and desert areas, leading to a significant number of deaths. Attempts to complete the construction of the United States Mexico barrier have faced stiff opposition from the Mexican government, various U.S.-based Chicano organizations, environmental organizations, and agricultural companies. About 45% of all agricultural laborers in the United States are illegal aliens, according to migration experts at the University of California, Davis.

According to Dr. Douglass Massey ( Smoke and Mirrors: U.S. Immigration Policy in the Age of Globalization, Russel Sage, 2001) and other experts, the efforts to curtail illegal immigration by means of security has done nothing but redirect the migration flows into the most desolate and desertic areas of the border, thus increasing the mortality rate of illegal immigrants. Furthermore, the security measures prevent the migrants re-entering Mexico, as they had done in the past. Instead, they remain in the U.S. for longer periods of time and eventually bring their families with them. President Bush, taking into account these findings, has presented an initiative to reinstate a Guest Worker Program to fill the needs of labor of the burgeoning American economy and, at the same time, has pushed to strengthen the security measures at the border to stop suspected terrorists and narcotics dealers from entering the U.S.