Which of the following was the first natural barrier to expansion of the frontier for american colonists?

one of the main reasons was definitely slavery. back in 1861, republican abraham lincoln was elected and ended up being a major influence in the slavery business. slavery greatly affected the texas economy because back in 1845 during the annexation of texas, slaves became a big part of the texas population. many texans that were in favor of the secession influenced groups through party ties.

when in doubt choose c

it's what my teacher told my class when we were going into psats