Answer:
The United States was reluctant to annex Texas because it did not want to fight a war with Mexico.
Explanation:
In 1836 the Republic of Texas was created, independent of Mexico. In August of 1837, Memucan Hunt Jr., ambassador of Texas in the United States, presented a proposal of annexation to Van Buren's administration. Believing that the annexation would lead to a war with Mexico, the US administration rejected the Texan proposal.
Finally, in 1845, James Polk became president and annexed Texas to the United States. This situation led to the Mexican-American War, as Van Buren had predicted.