美国内战的历史
创建一个包含五个外部资源的列表，这些资源可以提供有关给定主题的其他信息
1. History.com: https://www.history.com/topics/american-civil-war
2. Encyclopedia Britannica: https://www.britannica.com/event/American-Civil-War
3. National Parks Service: https://www.nps.gov/subjects/civilwar/
4. Smithsonian Institute: http://amhistory.si.edu/civilwar/
5. American Battlefield Trust: https://www.battlefields.org/learn/articles/american-civil-war