It’s a common trope in sci-fi books that the Earth has a unified World Government, and the aliens are similarly unified.

It’s not obvious that this would be the case though and in historical “First Contact” scenarios the fact that they weren’t unified made a big difference (think of the other groups in Mexico helping Cortes against the Aztecs, the various alliances European powers had with different North American tribes etc.)

Are there any books that consider this? Like imagine if First Contact happened at the height of the Cold War…