how did the united states purchase lands or rights from latin american countries for everyones benefit?

Answer 1

Because their governments sold the rights.
And it still continues in these times.
The US recently purchased the largest island off of the coast of the Baja Californis Sur from the governor of La Paz, Mexico.
Who then used the money to build and furnish his personal elaborate mansion.
Greedy, self-centered *******.

Answer 2

I don't understand the question. The US purchased a portion of what is today the southern part of Arizona (Gadsen Purchase) from Mexico for purpose of a railroad. The US ripped off Mexico of a huge part of their nation by war (Mexican Cession). We had the doctrine called Manifest Destiny and this meant occupying the lands from sea to shining sea regardless of others' rights to those lands. Such has always been the way of the world. No more blame on US then on everyone else in their respective histories.

Answer 3

The only purchase that I can think of in that regard is the Gadsden purchase, which was bought for the construction of a railroad thru New Mexico and Arizona.

http://en.wikipedia.org/wiki/Gadsden_Purchase