A more thorough explanation:

Definition: An enemy is someone or something that opposes or harms another person or group. It can also refer to a military force or a country that is at war with another country.

Examples:

• During the war, soldiers from one country were considered enemies by soldiers from the other country.
• John's ex-girlfriend became his enemy after they broke up and she spread rumors about him.
• The United States and North Korea are considered enemies because of their political differences.

The examples illustrate how an enemy can be a person, a group, or a country that is in opposition to another. In the case of the soldiers, they were fighting against each other in a war. In the case of John's ex-girlfriend, she was actively trying to harm him by spreading rumors. And in the case of the United States and North Korea, their political differences have led to a hostile relationship between the two countries.