The United States was once under an oligarchy government in the 1800's. true or false?

That statement is false.

Explanation:

Oligarchy is a system of government in which the power in the country is controlled by a small group of people (could be based on nobility, milltuiary, or education.)

Untied States was under an oligarchy government when the country is under the British' rule.  But, this occurred in 1700s, not 1800s.

USA gained independence from the British government in 1776 and the country has been run with a democracy system ever since.

it's

sir frederic attributed inaccuracies to schemas. memory reconstruction is one part actual events and one part personal schema, which can result in inaccuracies when memories are reconstructed.