Robert Bunting did not want to join the war effort initially. What event changed his mind?

The American Civil War

Explanation:

Robert Franklin Bunting was a Texas Presbyterian minister who established the "First Presbyterian Church of San Antonio."

Although he didn't want to join the war effort initially, the American Civil War changed his mind. As he left San Antonio towards the North, he didn't have any intentions to support the "Confederate clause," which marked white supremacy. He only wanted to go home and be reunited with his wife and child. Upon arriving at Bowling Green in Kentucky, he was prevented from crossing Ohio by the military. Owing to this, he accepted a command to become the chaplain of the Eight Texas Cavalry. He offered his pastoral services to one of the most popular regiments in the American Civil War.

So, this explains the answer.