@MontereyJack,
Lets understand something about those places.
Mexico ( I assume you mean the entire of Central America mainland ) is only that way because US dust cropped ( spray ) toxins on their crops. When those was imported into the United States tons of people who smoke weed got sick.
Again in Mexico in the past as with the invention of Peanut Butter ( Carver ), he had planned to open a plant in Mexico for processing. However he had to go to court to get it open.
St. Salvadorian warfare led to many of former military fleeing into the United States as refugees. Nobody helped them and discriminated and was racist towards them. Eventually these people evolved into the M-13 gang that was constantly in the news.
Haiti - Since the French withdraw after it was over-thrown by the slaves. Haiti was closed of for trade by many countries ( European / White nations ), and that is why it slipped into poverty. Only with help from Dominica Republic did Haiti actually stay afloat and traders willing to do business with the nation. Rap music and Haiti changing it's system of leadership in the 1990's is the greatest downfall of Haiti. If not then especially the earthquake which nobody did anything if anything to help them recover. That is why it is in the state that it is in today. In fact in terms of trade with Domonica via markets they prevent Haitians from going where they want asides one specific path. Many Haiti people still live in a form servitude where children are exchange and used as servants in other peoples houses, to even many becoming security or military. In the US however due to that fact many Haitians excel having living in harsh conditions. The former president of Nintendo parents are form Haitian military commanders and fled the nation fearing and knowing mindless war.
Guatemala - did not want the canal be built but the US forced via damaging the powers ( leader ) structure to get the Canal built. This caused tons of problems with Guatemala being able to live proficiently and normally, along with many other problems produced in South America itself.
United States did next to nothing to deal with the Mexican immigrants and allow them to fall into proverty and thus forming gangs.
United States gas the crops and then called it a drug problem after it was done. United States caused bad ( not good for consumption ) drugs to enter the nation and all this bs with the so called drug war ( which was still racism ).
United States ignored Haiti and rather friendship with France. Oh and with that Earthquake next to nothing was done. Even Puerto Rico got much attention and Dominica gets along with the United States.
United States caused the poverty of Guatemala with the construction of the canal not caring about that specific nation itself.