What was going on in the apartheid government during 1892-1994 that allowed the leader to take control?

During the 102 years that you refer to there was a lot happening.

You may want to be more specific.

In general, during the beginning of the period Britain consolidated control of the region, developed the mining industries, passed legislation to force Black people off the land into industrial work, established reservations for Blacks.

The country "The Union of South Africa" was created from the original 4 countries and became self-governing in 1910.

The government from 1910 to 1994 was white controlled. Although policies in the era 1910 to 1950 were racially biased, so called "Grand Apartheid" blossomed in the 1960's after the country gained full independence from Britain as "The Republic of South Africa".

In the late 1980's, after decades of economic sanctions and guerrilla warfare it became clear that Apartheid was not sustainable and negotiations with the African National Congess began.