Once nominated by the president, cabinet appointees (such as the secretary of defense) must be and can be

The answer is: Confirmed by the senate; fired without the senate's approval.

The purpose of the confirmation is to give enough time for the senate to do a background check on the cabinet appointees and decide whether to vote for their appointment or not. If after the background check the senate found something wrong with the appointees, the senate can fire the appointees through voting.

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.