Having looked up the meaning of the word, it doesn't make much sense to me why the verb 'forge' is used in the following sentence:
"Peace on this planet will not be forged by military strength."
In this case "forged by" just means "reached by/through", "obtained with/through:", "achieved through", etc.
To literally forge something is to create it in a blacksmith's shop (also called a forge), i.e. to work raw iron at high temperatures into a tool, heating it, beating it, reheating, shaping, cooling, etc. until it becomes a strong, highly crafted end product. So the figurative meaning of "forge" reflects that, and implies the creation of an end product through a long process involving lots of effort, manipulation, and hard work.
That's the kinda explanation I was after. Thanks