What do you think was the most important factor behind the closing of the American fronter the discovery of mineral resources, government and grants and promotions or the completion of the railways ? Use evidence to support your answer .

government

Explanation:

In 1890 the Census Bureau broadcast the. closure of the frontier

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.  

either b) they were often feared and despised by other native cultures. or

c) their obsession allowed them to coexist with many other native cultures because of their peaceful nature.