Theory:

 
A metaphor is a figure of speech that makes an implicit, implied, or hidden comparison between two things that are unrelated, but which share some common characteristics
 
Metaphors are used to dramatize thoughts to emphasize and elevate the expression to a higher intensity.
 
Metaphors have comparison which is indirect. For instance, the sentence, "Riya is like a tigress" is a simile and the sentence "Riya is a tigress" is a metaphor. While both the sentences mean the same, we can easily understand that "Riya" is compared to a tigress in a more prominent and direct tone in the first sentence. In the second sentence, it looks as if the speaker is saying that Riya is a tigress rather than she looks or behaves like one.
Example:
1. The calm lake was a mirror- In the real sense, the lake cannot be a mirror. However, it can have the qualities of a mirror. It can stay still and can reflect things. Hence, the sentence means that the calm lake was able to reflect things very clearly.
 
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The reflection of the tree seen on the lake is as good as the ones seen on mirrors 
  
2. Chaos is a friend of mine- The literal meaning claims that 'chaos is a friend of the speaker'. The metaphorical meaning is that 'chaos has been a part of the speaker's life for a long time'.
 
3The sun is a golden ball - The sentence doesn't mean that sun is ball made of gold or that you could run around and play with it. It actually means that 'the sun is in the colour of gold (or fire) and is in the shape of a ball.
Metaphors used in the poem "No Men Are Foreign":
  • Beneath all uniforms, a single body breathes - Uniforms in the line stands for the army/militaries of different countries. The poet indirectly states that every human being, even if it is a soldier, is equal. Their uniform may be different in size, shape or colour but the emotions of people wearing them are the same.
  • Are fed by peaceful harvests, by war’s long winter starv’d - In this line, the harvest that is dry during winter is compared to the hunger and starvation experienced during a war. Just like winter, the resources are reduced during a war.