Final answer:
Presidents Jackson and Van Buren opposed the annexation of Texas due to concerns about a potential war with Mexico, economic impact, and its constitutionality.
Step-by-step explanation:
The main reason for Presidents Jackson and Van Buren opposing the annexation of Texas was that they believed it would cause a war with Mexico. They were also concerned about the economic impact of annexation, as it might lead to tension and conflicts with other nations. Additionally, they believed that the annexation of Texas was unconstitutional, as it violated the doctrine of states' rights and could set a precedent for the expansion of slavery.
Learn more about reasons for opposing the annexation of Texas