populous, populace

Populous or populous describes an area having a large population, meaning a lot of people living in it--
The town was not as populous after the factory closed.
Toxic waste should be treated far from any populous area.

Populace or populace ( rhymes with populous ) means the inhabitants or citizens of a particular place--
The outlaws of the old west often terrorized the populace.
The health department worried about the disease spreading among the populace.

Now that you know that, you can say--
"The dictator knew that the entire populace of such a populous area would never go along with the scheme."

Note--"population" may mean the inhabitants of an area or region. In this way it is a synonym for populace, but "population" is usually used in a more abstract way, as in the census--
The health department worried about the disease spreading among the population.
"Population" may also refer to animals or other living things, as in the population of butterflies in a meadow.

 Note # 2--"populate" means to provide with inhabitants, as in a colony or new territory--
It took many years for the Americans to populate the west.
"Population" may be a noun ( thing or idea ) form of "populate"--
The population of the west took many years.

Note # 3--"populist" is a political term for someone who believes in appealing to the common people--
His parents believed  the elite should make decisions. They despised his populist sympathies.