The main reason why history is open to ongoing and changing interpretations is because new facts are always being discovered about the past, which allows people to change their opinions regarding how things happened throughout history.
The Mississippi River was a long trail of flowing water. Erie Canals were made to be long and help water travel to help crops and plants grow. Hope I helped! :)
The Soviets were setting up nuclear missiles in Cuba. This meant that they were now able in theory to launch a nuclear missile directly at large parts of the USA and it was therefore viewed as a threat by the USA. I hope that helps.
