The trade between United States and Mexico started in late 19th century after the Mexican revolution. The trade relationship between US and Mexico was good as the United States was investing more in Mexican business.
U.S was trading oil from Mexico as it is the most crucial thing for the United States. More these two countries are part of NAFTA (a trading agreement) along with Canada. Due to this treaty between three countries, the countries are free from trade barriers.
Answer:
D. to prevent the spread of communism to South Vietnam