Although its territory has been inhabited since the Paleolithic Era, modern Angola originates in Portuguese colonization, which began with, and was for centuries limited to, coastal settlements and trading posts established from the 16th century onwards. In the 19th century, European settlers slowly and hesitantly began to establish themselves in the interior. As a Portuguese colony, Angola did not encompass its present borders until the early 20th century, following resistance by groups such as the Cuamato, the Kwanyama and the Mbunda. Independence was achieved in 1975 after a protracted liberation war. That same year, Angola descended into an intense civil war that lasted until 2002. It has since become a relatively stable unitary presidential republic.