Why wasn't Liberia colonized?

In a way, it was - though not officially by another country. Liberia was set up as a place where freed slaves from the USA could rule themselves. An American society under president Monroe bought land there and paid for freed slaves who wanted to go to be transported there.

The "colonization" started in 1816, and Liberia became independent in 1847. However, the country called Liberia included some land held by the indigenous people, who had been living in the area before the freed slaves arrived (known as Americo-Liberians or Americo- Libe). So there was always tension between the two groups, and the government was dominated by Americo-Liberians until 1980 - the indigenous people didn't get votes until 1951. (Since the same party ruled for 133 years, it was often said that Liberia had the most stable government in the world.)

Many of the Americo-Liberians viewed themselves as an elite, and better than the native people and not as part of the general populace. - People from other ethnic groups were often called "natives". For this reason, Liberia could be said to be a colony without a country to be colonized from!

(See en.wikipedia.org/wiki/History_of_Liberia )