How did violence dominate life in the USA in the 1920's?

Answer 1

During the 1920’s, racial tensions in American society reached boiling point. New non-protestant immigrants like Jews and Catholics had been arrived in their masses from south-east Europe since early on in the century. Together with Orientals, Mexicans and the Black population these minorities suffered the most at the hands of those concerned with preserving the long established White Anglo-Saxon Protestant (W.A.S.P.) values that were an integral part of American life. Prejudice and racism reared its ugly head in many areas of society, with people showing a tolerance for racist views in the media, literature and towards organisations like the Ku Klux Klan.
http://www.planetpapers.com/Assets/2047.php

You also had prohibition and gangsters. It was known as the lawless decade:
This is one of the reasons--only one--why we call it the Lawless Decade. The law that had the greatest impact on the wide and wonderful land evoked the least obedience from the people. Liquor--good, bad, indifferent or deadly--flowed like a giant waterfall all during the thirteen wobbly years of the thing Herbert Hoover called "an experiment .. noble in purpose." But the bootlegger was not alone; he dealt only in the happy juice. His errands made Prohibition a sopping-wet farce but there were many other laws ground into the dust during the vibrant and tumultuous years from the Armistice to Repeal. Criminal laws, moral laws, civil laws, social laws, political laws, religious laws--name them.

The convulsive shocks of The Twenties left very little unturned as the once-sacred barriers of tradition and custom were broken down. For better or worse, the populace would never again be inhibited by its own past. All the old playing rules went out of the book.
http://www.lawlessdecade.net/intro.htm

Answer 2

What makes you think that violence dominated American life in the Nineteen Twenties?

I've never heard that idea.

Is that a homework assignment?

What the heck are they teaching you kids in public school, anyway?