What influences a country having, or not having, an official language?
Politifact mentions that there are 14 countries without an official language:
There are 196 nations, according to infoplease.com, an online almanac. The CIA lists no official language for 14 of them. Aside from the U.S., they are American Samoa, Australia, the Czech Republic, Denmark, Holy See, Iceland, Jamaica, Japan, North Korea, South Korea, Mexico, San Marino and the United Kingdom.
There doesn't seem to be much in common with regards to the countries that lack an official language. Some of them are democracies (the USA, Australia, South Korea), one of them is a totalitarian state (North Korea), the national languages differ (English, Japanese, Korean), and the culture of the peoples differ (some are predominantly Christian, while at least one is predominantly Buddhist).
Does a country being fairly monolingual affect whether or not a country has an official language? I assumed it would, but some countries have a single official language - only 101 out of 178 countries have more than one official language (yes, that 178 countries is different from what Politifact is saying - "what is a country?" may be a difficult concept)
Does the degree of nationalism of a country affect it? Are there any other factors?