Answer:
Since the 13th amendment banned slavery, plantation owners in the south would have been outraged since they lost all of their minimal cost labor force.
Bombing would make the most sense. This was carried out during Kosovo's war for independence
Good luck!
Triple entente
1. France
2. Russia
3. Great Britain
Triple alliance
1. Germany
2. Austria-Hungary
3. Italy
1 is the answer to your question.