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Eg; Say you killed someone's brother in A random task. You may earn an event - the anger of the brother. and thus opens the ability for someone to invade a topic as that persons brother.
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To qualify to be an invader one must have proven activity, and will get rewards for being an invader.
Obviously any invaded topic will give the invaded additional rewards...
I have prob written this out baddy but i'm going to assume your Iq is higher than mine thus you get this..