Answer:
Correct answer is Superior military leadership .
Explanation:
First option is not correct that although most of the people supported the cause, it wasn't seen as a major advantage during the war.
Second option is not correct as it is believed that Confederacy had better generals, which was an important factor especially at the beginning of the war. But, later things changed, because North prevailed using its technological advantages.
Third option is not correct as European forces didn't interfere in the war.
Last option is correct as North had more soldiers, was more developed technologically and this proved to be major factor.
