Wild West

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The western United States during the period of its settlement, especially with reference to its lawlessness.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun The western United States during the 19th-century era of settlement, commonly believed to be lawless and unruly.
• proper noun by extension A place or situation in which disorderly behavior prevails, especially due to a lack of regulatory oversight or an inadequate legal system.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the western United States during its frontier period