A dyad is a social group conformed by only two people. It can be based on a romantic interest, family relation, partnership, friendship, etc. <em>They can be unestable because both members must cooperate at the same level </em>and they can also be emotionally intense.
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The only change I know of was the silk road, where they had to build roads and clear forests so that traders could go through. I don't think any other geography changed during that era.
