How did the spread of disease contribute to the decrease in native americans populations?

When the Europeans came to America they brought along diseases such as smallpox or measles. The Native American's have never dealt with these diseases before making them (unlike the Europeans) not develop an immunity towards it. These diseases ended up killing the majority of the native American population.

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.