system
Given the following post, respond as if you're commenting on Reddit:
human
[General Sci-Fi] With as diverse as Earth is with languages, religions, races, and ethnicities, why are other planets so homogeneous?

When we watch sci-fi, other planets are generally shown to have only one language, one race, and one religion. What makes Earth special in its cultural diversity?
gpt
Primitive planets are generally very diverse, because of the large travel times between different parts of the planet. Your other posts lead me to believe you're talking about earth at the turn of the twentieth century, when it was rapidly homogenizing. During this period most people on the planet speak one of only four language (Arabic, English, Spanish, Mandarin).

Predictive models give it between two and five hundred years (local) before most of the planet speaks one language and is unified under a single planetary government.