There are very prosaic reasons for the popularity of UFO sightings in the USA. 1. The gdp per capita per cloudless land area is far higher than anywhere else.

There are very prosaic reasons for the popularity of UFO sightings in the USA. 1. The gdp per capita per cloudless land area is far higher than anywhere else. Africa and Australia have lots of empty sky but relatively no-one is out and about during night time. Plus USA does some have some interesting weather. So the opportunities to see anomalous (yet very terrestrial) phenomena is high. 2. The concern that comes from being the richest and most powerful country in the history of the world, that others are trying to infiltrate. (I was almost going to use fear or paranoia instead of concern, but some of the concern is warranted) 3. USA is the center of world culture. Everything American is amplified via Hollywood and music.