When the colonial powers carved up Africa, the divisions between the countries bore virtually no resemblance to the traditional areas of the various ethnic groups, many of which therefore ended up split between two or more countries. As you will see, there are cultural differences between the groups in different parts of Namibia, but they are only a little more pronounced than those between the states of the USA, or the regions of the (relatively tiny) UK.
There continues to be a great deal of inter-marriage and mixing of these various peoples and cultures – perhaps more so than there has ever been, because of the efficiency of modern transport systems. Generally, there is very little friction between these communities (whose boundaries, as we have said, are indistinct) and Namibia's various peoples live peacefully together.
In Namibia, which is typical of any large African country, historians identify numerous ethnic groups. The main ones are detailed below, arranged alphabetically. Apart from Afrikaans, their languages fall into two main families: Khoisan and Bantu. The population sizes given are based on surveys done during the 1980s, and adjusted according to estimated average growth rates since then.