Attack on Titan: Why Did Eren Start the Rumbling?

Why did the rumbling happen?

The world’s ignorance and refusal to entertain diplomatic talks with Paradis played a pivotal role. It was the most significant factor that led Eren to initiate the Rumbling. Eren discovers the existence of human civilization outside the walls. Eren also learns that people refer to the inhabitants of Paradis as Devils. They are seen as a threat to the existence of humanity. This perception has persisted for centuries since the 145th Fritz King retreated inside the Walls, effectively dissolving the Eldian Empire of the past.