4) Which of these is a reason President William McKinley advocated going to war with Spain in 1898?

I think it is because Mckinley wanted to keep Cuba safe because of business and economic development. The US had been investing a huge amount before the war. With the ongoing war between Spain and Cuba, there is a possibility that some investments would eventually pull out because it was no longer safe to do business in that region. So Mckinley wage war against Spain if they don't pull away their troops in Cuba