STELLENBOSCH, South Africa — One cold morning, Stefan Smit, a white farmer in South Africa’s stunning wine region, woke up to find his vineyard under siege.

Anxious and angry, Mr. Smit, 62, drove his pickup truck to the highest point on his estate and peered down. Impoverished residents from the black township next door had stormed the land, clearing weeds and erecting 40 shacks in a matter of hours.

“I, personally, can’t breathe here,” Mr. Smit said later.

Virtually overnight, Mr. Smit’s farm, with its sweeping views of the Stellenbosch region, became a battleground in a bitter political fight that has split the nation and reached all the way to the Trump White House: Who should own South Africa’s land?

The fight pits white South Africans, who still control much of the economy a generation after the end of apartheid, directly against their black neighbors, many of whom are struggling to acquire a tiny patch on which to build a shack.