Final answer:
Texans seceded from the Union primarily due to issues surrounding states' rights and slavery, believing the United States had abused its power.
Step-by-step explanation:
The reason that Texans gave for seceding from the Union was mostly centered around the issue of states' rights and the desire to continue the institution of slavery. Texas, along with other southern states, seceded following Lincoln's victory in the presidential election. Secessionists justified their actions by claiming they were defending their 'liberty,' a liberty heavily tied to states' rights and their right to own slaves as property and to take that property anywhere in the country.
This action was part of a broader sentiment among southern states that wished to preserve their way of life, including the institution of slavery, which they believed was under threat from the political and social movements in the North. Therefore, the correct answer to why Texans seceded from the Union is A. The United States had abused its power, specifically in regards to states' rights and issues pertaining to slavery.