This statement is completely true, the native peoples to the Americas were introduced to diseases such as smallpox which wiped out a majority of the populations. While battles and such took place this was a huge cause of change because of the effectiveness. Positively, however, the natives were also introduced to the trading of European goods such as foods, guns, and livestock, and particularly horses.
The ultimate goal was the overthrow of Castro and the establishment of a non-communist government friendly to the United States.
The third part of James k. Polk's war plan was to "1.) to capture Mexico city". This fell outside Polk's usually craving for manifest destiny, which up until then have only been an east-to-west route.
We need a picture to be able to help you