What conflict is often referred to as the War of Northern Aggression by some?

The term "War of Northern Aggression" is historically associated with the Civil War, particularly from the perspective of those in the southern United States. This phrase reflects a viewpoint that characterizes the conflict as an invasion or aggression by the northern states against the southern states. The Civil War, which lasted from 1861 to 1865, was fundamentally about issues such as states' rights, slavery, and economic differences, leading to a deep-seated division between the North and South.

In contrast, the other options do not share this specific terminology or interpretation. The Spanish-American War involved the U.S. against Spain in 1898 over imperialist goals rather than a conflict rooted in regional division within the United States. The Mexican-American War, which occurred in the mid-19th century, primarily dealt with territorial disputes between the U.S. and Mexico, without the sectional strife characteristic of the Civil War. World War I, fought from 1914 to 1918, involved many nations globally and again does not relate to the internal conflict and regional perceptions that the Civil War embodies. Therefore, "War of Northern Aggression" is a term distinctly tied to the Civil War.