Answer:
There are a few reasons:
1. It creates generally good diplomatic practices. If you are trading with another state, then typically you will have a good relationship with them later down the line.
2. Some states did not have access to resources that other states had access to. For example, gold was extremely wanted by many European states, so other states such as ones in the Middle East would provide those resources for resources the Europeans could offer.
3. It spread not only metals, but also knowledge and religion. The spread of these things actually caused these large states to take other state’s religions and knowledge into account. Some incorporated the religions, some banned it!
