Why has no empire taken over the whole world?

No empire has taken over the whole world due to a combination of geographical, cultural, and technological factors. Geographical barriers like oceans, mountains, and deserts have historically limited expansion. Additionally, diverse cultures and societies often resist conquest, leading to strong local identities that challenge imperial authority. Lastly, advancements in technology and communication have empowered nations to resist domination and fostered global cooperation, making total conquest increasingly impractical.