Think of it like this Internal: A force inside yourself External: A force outside of yourself So if there an external force, it’s a force from outside so an example would be bullying. You wouldn’t want to go where you are being bullied so that would be an outside force affecting you.
Answer: Simply because he believes that someone has to fight for Tom, and no one else would do it.
Explanation:
Atticus was not only defending Tom Robinson in the case, but also against all the racist people who believed he was guilty just because he had coloured skin. Atticus was trying to show her daughter that some causes, though lost, should be defended.
