“America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves” is a quotation frequently attributed to Abraham Lincoln (1809-1865), but he never said it. Lincoln addressed the Young Men’s Lyceum of Springfield, Illinois on January 27, 1838,  giving a speech titled “The Perpetuation of Our Political Institutions,” stating:
 
“Shall we expect some transatlantic military giant to step the ocean and crush us at a blow? Never! All the armies of Europe, Asia, and Africa combined, with all the treasure of the earth (our own excepted) in their military chest, with a Bonaparte for a commander, could not by force take a drink from the Ohio or make a track on the Blue Ridge in a trial of a thousand years. At what point then is the approach of danger to be expected? I answer. If it ever reach us it must spring up amongst us; it cannot come from abroad. If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time or die by suicide.”
 
Joseph McCarthy (1908-1957) produced a fake Lincoln quote in November 1953 when McCarthy addressed the nation and said:
 
“As Lincoln said, ‘From whence then will danger come? If this nation is to be destroyed, it will be destroyed from within, if it is not destroyed from within, it will live for all time to come.’”
 
“America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves” has been cited in print since at least 2002, but does not appear to date anywhere close to Lincoln’s lifetime.
 
   
Wikipedia: Abraham Lincoln’s Lyceum address
Abraham Lincoln’s Lyceum Address was delivered to the Young Men’s Lyceum of Springfield, Illinois on January 27, 1838, titled “The Perpetuation of Our Political Institutions”. In this speech, Lincoln spoke about the dangers of slavery in the United States, as the institution could corrupt the federal government.
 
The speech
The subject of Lincoln’s speech was citizenship in a democratic republic and threats to American institutions.[1] In the speech, Lincoln discussed in glowing terms the political system established by the founding fathers, but warned of a destructive force from within. He asked his listeners:
 
Shall we expect some transatlantic military giant to step the ocean and crush us at a blow? Never! All the armies of Europe, Asia, and Africa combined, with all the treasure of the earth (our own excepted) in their military chest, with a Bonaparte for a commander, could not by force take a drink from the Ohio or make a track on the Blue Ridge in a trial of a thousand years. At what point then is the approach of danger to be expected? I answer. If it ever reach us it must spring up amongst us; it cannot come from abroad. If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time or die by suicide.
 
3 January 1941, Cedar Rapids (IA) Tribune, “Observations of a Veteran” by Matthew Couden, pg. 2, col. 4:
The former civilizations end nations that have succumbed to conquerors have been destroyed by from the outside; our present civilization, if it is destroyed, will more likely destroyed by the barbarians on the inside.
   
Google Books
Caesar and Christ:
The Story of Civilization (Volume III)
By Will Durant
New York, NY: Simon and Schuster
1944
Pg. ? (“Epilogue: Why Rome Fell”):
A great civilization is not conquered from without until it has destroyed itself within.
 
25 November 1953, San Diego (CA) Union,“McCarthy Speech As Broadcast Across Nation,” pg. A-5, col. 6:
“As Lincoln said, ‘From whence then will danger come? If this nation is to be destroyed, it will be destroyed from within, if it is not destroyed from within, it will live for all time to come.’”
 
Google Books
Joseph R. McCarthy
By Allen J. Matusow
Englewood Cliffs, NJ: Prentice-Hall
1970
Pg. 81:
As Lincoln said: “From whence then will danger come? If this nation is to be destroyed, it will be destroyed from within, if it is not destroyed from within, it will live for all time to come.”
     
DSLReports.com
Murray3
2002-04-03 07:47:43
(...)
“America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves.” - Abraham Lincoln
 
4 July 2002, Fort Worth (TX) Star-Telegram, “A gift to guard,” Metro, pg. 10:
“America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves.”
   
LewRockwell.com
July 10, 2002
Fake Lincoln Quotes
by Thomas J. DiLorenzo
(...)
Lincoln supposedly warned that “If this nation is to be destroyed, it will be destroyed from within; if it is not destroyed from within, it will live for all time to come.” Another fake Lincoln quote.
 
St. Petersburg (FL) Times
More than just emotion
Shared ideals unified us after Sept. 11; misplaced zeal cannot be permitted to splinter commitment to those ideals.
By ABDULLAH AL-ARIAN
published September 9, 2002
(...)
Abraham Lincoln once said, “America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves.”
 
28 December 2003, The Gazette (Colorado Springs, CO), “Quote, Unquote,” Metro, pg. 6, col. 4:
“America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves.”
ABRAHAM LINCOLN
 
Modesto (CA) Bee
Friday, Feb. 17, 2012
SATURDAY SHORTS: Wise words from a pair of presidents
(...)
“America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves.”
(Abraham Lincoln—ed.)