Answer:
Politics
Step-by-step explanation:
The most significant change in the late 18th and early 20th centuries is POLITICS.
This is evident in the crucial incidents that arose throughout the world, most especially in Europe and America or New World.
To illustrate better, there are tremendous effects French Revolution of 1789, in Europe as the government of many nations was changed, new rules to govern people were also changed, and many more.
The comparable occurrence in the early 20th century is the World War 1 impact on the government, imperialism, and other political issues surrounding nations of the world.