White supremacists who commit these terrorist acts like the recent Buffalo massacre collectively believe in the “great replacement theory” (GRT) — a conspiracy that Jews & elites are replacing white people with non-Europeans. This myth is based on a distortion of statistics, pseudohistory, and white supremacism.
Declining birth rates for whites and immigration fears are driving GRT. Let’s look at the demographic transition model. This model assists with understanding and predicting demographics by analyzing birth rates and death rates. The model has five stages.

Stage 1: Before the Industrial Revolution, both birth rates and death rates are high, so the population remains relatively consistent — with the obvious exception of plagues and natural disasters.