Final answer:
Isaac Stevens served in the Mexican-American War and was Washington's first territorial governor. However, he did not choose Seattle as the territorial capital and fought for the Union during the Civil War.
Step-by-step explanation:
Isaac Stevens served in several important roles during his lifetime, but some statements about him need clarification:
He did serve in the Mexican-American War, so this statement is correct.
Isaac Stevens did not choose Seattle to be the territorial capital; instead, he chose Olympia.
Regarding his service during the Civil War, Isaac Stevens fought for the Union, not the South, and was actually killed in action while serving as a major general for the Union.
Furthermore, he was indeed the first territorial governor of Washington.