After Japanese attack on Pearl Harbor on December 7, 1941 most of the countries of Central and South America cooled relations with Axis countries. Following the cooling of relations, most countries of Central and South America released that they are now dependent on the United States for trade. Needs of the USA during the war disrupted further trade. United States needed varius products from some Latin-American countries (e.g. Platinum from Columbia and cotton from Chile). Prices were agreed upon, but countries lost their ability to trade in open market.
Shortages of consumers goods were also a great problem. The demands of the American war industry reflected on availability of products required for everyday life. Their price increased and they were very difficult to find. All of these reasons caused inflation.
Most of Latin America used the reasons listed above to their advantage by siding with the United States and receiving aid.
On March 21, 1942 the United States government enacted Lend-Lease, which was a program which gave war materials and other benefits for countries in exchange for participating in war.
Altough Latin America received only $400 million in war materials, lot of the countries, especially Brasil profited. Brasil was pretty important to Allied forces mainly because of his geographical position. It was northeast corner of South America, allowing patrolling between West Africa and South America. It was used as providing a ferry point for the transfer of American-made war materials to the Allies fighting in North Africa, but also because it was seen as a possible German invasion route that had to be defended.
Some other countries like Columbia, Panama and Ecuador also received military aid mostly for building military bases.
Unlike Brasil and other countries, Argentina and Chile received very little military aid, mostly because for most of the war neither would heed American demands that they sever all relations with the Axis powers.