What did richard current mean when he described the civil war after the summer of 1863 as a "war of attrition"?

Why were presidents andrew jackson and martin van buren unwilling to annex texas? a. they did not want texas to be admitted to the union as a slave state. b. they feared that the annexation of texas as a slave state would lead to political problems within the union. c. they thought that texas was too large to be admitted to the union as one state. d. they did not believe in the idea of manifest destiny.