While racial segregation in Soth Africa had existed in one form or another for generations, it became codified into law in 1948. There are a number of reasons for this. Let's look at some of them.

A major precursor to what would become apartheid was the Glen Grey Act of 1894. This law eliminated communal land rights. Thousands of black South Africans were forced off of their tribal land as a result of the act. In 1913, the Native Land Act established tribal reserves. These laws set up much of the framework that dictated where South Africans could live based on race. In many ways, the apartheid laws that began in 1948 were built off of these established legal frameworks.

Before WWII, most black South Africans lived in rural areas. Rapid growth and industrialization created many new job opportunities in the cities. This attracted many rural black people to places that had historically been white areas. The government made very few accommodations to allow for this huge influx in terms of social services or adequate housing. To compensate, black people became more politically influential in these urban centers. Many white people felt the status quo to be threatened by their migration. Afrikaner nationalists used this perceived threat to galvanize political support for themselves.

This led to the rise of the National Party, which won a majority of legislative seats in 1948. Once in a position to draft and pass legislation, the National Party set about dividing up the country along racial lines. Their party platform was that South Africa did not comprise a single unified nation. Rather, it was a conglomeration of different racial entities. While the first grand apartheid law would not be passed until 1950, the National Party wasted no time creating laws and ordinances that divided the races up into separate townships. This put in place the foundation of what would soon become apartheid.