2. How did empires expand their influence and strengthen their control over existing territories from ca. 1750 to ca. 1900?

The Modern Period in AP WORLD: MODERN covers from 1750-1900 CE. This is very heavy on economic, social, and political change. The next two of the nine units in AP WORLD: MODERN are featured in this time period. See the chart below for the exact weighting

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.  

a social contract.

"a social contract is an agreement between citizens and their leader where the citizens give up certain freedoms in exchange for protection. the constitution of the united states is an example of a social contract."