“Sabre-rattling” (also spelled “saber-rattling”) is when a person or a government threatens to use force against another, just as a soldier rattles a sabre against an enemy. “Sabre-rattling” was commonly associated with Germany in the 1910s, both before and during World War I.
 
The term “sabre-rattling” has been cited in print since at least 1886. “Saber rattling” was used in a newspaper headline in 1908 and “sabre-rattling” in a newspaper headline in 1909. The Kölnische Zeitung (Cologne Gazette) used the term by at least the 1900s and possibly popularized “sabre-rattling” at an earlier date.
   
   
Wiktionary: sabre-rattling
Alternative forms
saber-rattling (mostly US)
Etymology
From the early 20th century, when an officer would threaten to draw his sabre.
Noun
sabre-rattling (uncountable)
1.(idiomatic) A flamboyant display of military power as an implied threat that it might be used.
2.(idiomatic, figuratively) Any threat, such as one company threatening another with a lawsuit.
 
Wikipedia: Saber noise
Saber-noise or saber-rattling (Spanish: ruido de sables) may be used to refer to a historical incident in Chilean history that took place on September 3, 1924, when a group of young military officers protested against the political class and the postponement of social measures by rattling their sabers within their scabbards. This is not the origin of the phrase, however; in speaking at an American Congressional hearing of the need for Pacific coast fortifications to address the rising militarism of Japan, on February 21, 1921, Congressman John F. Miller made repeated reference to Japan as the place “where the saber is rattling”, and it is apparent that it was regarded as a common figure of speech at the time.
 
The term is now applied generally to cover any indication of military aggressiveness. In a sense, strategically timed war games can serve as an explicit form of saber-rattling, in that the extent of a country’s military muscle is put up on display for other countries (namely, adversaries) to see.
   
The Free Dictionary
Noun 1. sabre rattling - the ostentatious display of military power (with the implied threat that it might be used)
   
Free Merriam-Webster Dictionary
saber rattling noun
Definition of SABER RATTLING
: ostentatious display of military power
First Known Use of SABER RATTLING
1922
 
(Oxford English Dictionary)
sabre-rattling n. military aggression; threatening violent action; aggressive blustering; also as adj.
1922 Weekly Dispatch 19 Nov. 8   A policy of adventure, sabre-rattling, and reckless expenditure.
1928 Observer 26 Feb. 16/4   A sabre-rattling gesture against a nation with whom we have been at peace for more than a hundred years.
1958 H. M. Hayward & M. Harari tr. B. Pasternak Dr. Zhivago i. iv. 105   You have to swagger about in an officer’s uniform too, you have to do your own bit of sabre-rattling.
     
Google Books
Prince Bismarck:
An historical biography, Volume 1
By Charles Lowe
New York, NY: Cassell & Co.
1886
Pg. 486:
Germany, in fact, could not mind her business, nor tranquilly sleep, nor eat her food in peace, for the incessant sabre-rattling of France.
     
1 June 1900, Westminster Budget (London), “Here, There, and Everywhere,” pg. 30, col. 1:
There is some talk of constituting a special “League of Arbitration” amongst the journalists; and a few enthusiasts are even sanguine enough to propose that a sort of “pledge” to abstain from journalistic militarism and sabre-rattling should be offered to penmen, not unlike the Temperance pledge.
 
Chronicling America
1 April 1899, The Times (Washington, DC), pg. 1, col. 3:
DENOUNCED AS BRUTAL.
The “Cologne Gazette’s” Severe Comment on the Samoan Affair.
(...)
The “Gazette’s” is the most severe comment that appears among the weighty German journals, which generally continue their moderate tones. The Jingo press, on the other hand, is doing a great deal of sabre-rattling, their indignation being mainly directed against Great Britain, notwithstanding the fact that Admiral Kautz, the American commander, took the lead in precipitating the bombardment.
 
25 February 1908. Springfield (MA) Republican, pg. 8, col. 6:
SABER RATTLING HEARD AFAR.
[From the Providence Journal.]
Some German observers are disposed in regard certain remarks of Secretary Taft on his New England tour as “saber rattling,” intended to impress Japan.
   
17 May 1908, Chicago (IL) Daily Tribune, pg. A1:
WAR LORD RATTLES HIS SWORD AGAIN
Kaiser Semi-Officially Warns Nations That German Saber Is Loose in the Scabbard.
When the kaiser rattles his sabre the whole world immediately pays attention. He has several ways of doing it. Sometimes it is by sending a semi-private dispatch to a foreign ruler, as in the case of the Kruger telegram.
   
Google Books
October 1908, The Navy, pg. 14, col. 1:
There is far too strong a tendency among the young German element towards “sabre-rattling” tactics and tall talk, coupled with an astounding ignorance of other nations’ fighting resources.
 
21 March 1909, Montgomery (AL) Advertiser, pg. 20, col. 5:
POWERS ARE WARNED.
German Papers Print “Sabre-rattling” Article About Austria.
Berlin, March 20—Both the “North German Gazette” and the “Cologne Gazette” have published semi-official “sabre-rattling” articles, warning other powers of the danger of interference in a settlement between Austria and Servia.
 
Google Books
Historical Backgrounds of the Great War
By Frank James Adkins
New York, NY: McBride, Nast & Company
1915
Pg. 90:
Every State has neighbors across its borders; but Germany’s tradition has been to remind her neighbors of her presence by sabre-rattling.
   
Google Books
General von Sneak:
A little study of the war
By Robert Blatchford
New York, NY: Hodder and Stoughton
1918
Pg. 34: 
War is part of the policy. That is the idea behind the (Pg. 35—ed.) sabre-rattling of German diplomacy.
   
OCLC WorldCat record
Taiwan: China’s sabre-rattling has mixed impact
Publisher: Hongkong [Review Pub. Co. Ltd., etc.]
Edition/Format:  Article : English
Publication: Far Eastern economic review. 158, no. 32, (1995): 20
Database: ArticleFirst
 
Evening Standard (London)
Iran’s sabre rattling could turn into war with West at any time
Robert Fox, Defence Correspondent
5 Jan 2012