On August 3, 1914, Great Britain sent an ultimatum to Germany not to invade Belgium. The next day, German troops were in the neutral country and Great Britain declared war. Great Britain's reasoning was that Belgium was an independent, neutral state whose existence and sovereignty was guaranteed by Great Britain, France, Russia, Austria, and Germany. It's creation dates back to the Treaty of London, signed in 1839. The German Chancellor referred to this document as a "scrap of paper." Modern critics of Britain's decision to go to war on behalf of Belgium trivialize the treaty as a "seventy-five-year-old treaty," giving the impression that it was too old to still have value. By doing this, critics ignore 75 years of Great Britain's, France's, and even Germany's efforts to ensure that Belgium's neutrality was never violated. By examining these seven-plus decades of treaties, declarations, and diplomatic correspondence, it can easily be shown that the neutrality of Belgium was much more than a "scrap of paper" and was actively cared for by the original guarantors, especially Germany.
Prior to 1839, Belgium was not a recognized country. When the Treaty of London was signed on April 19, the kingdoms of Great Britain, Austria, France, Prussia, and Russia officially recognized the state and Belgium was "placed under the guarantee" of these countries. Great Britain and the Netherlands gave up territory in the process. The treaty is a lengthy one which goes through the details of boundaries, duties, and debt. The most important part is found in Article VII which states "Belgium, within the limits specified in Articles I, II, and IV, shall form an independent and perpetually neutral State. It shall be bound to observe such neutrality towards all other States."
Focusing on the age of the Treaty of London is misleading since there were other treaties which cited and reaffirmed it. For example, 41 years later, Belgium's neutrality became a hot topic when the Franco-Prussian War broke out in the summer of 1870. Consequently, Prussia and France each signed separate treaties with Great Britain proclaiming that Belgium's neutrality would not be violated. The key to these treaties was that both Prussia and France were compelled to make these declarations. In the Prussian treaty, signed on August 9, the king declared that "it is his fixed determination to respect the neutrality of Belgium, so long as the same shall be respected by France. . ." On August 11, the king of France signed a treaty with Great Britain making the same declaration. Great Britain declared in each treaty that if one side violated Belgium's neutrality, Britain was prepared to cooperate with the opposing side. The island was not picking a side, but clarified that her involvement would not go "beyond the limits of Belgium, as defined in the Treaty between Belgium and the Netherlands of April 19, 1839." These treaties with Prussia and France were only valid until the Franco-Prussian War ended on May 10, 1871.
After the war, the German Empire was established with Prussia as the leading state. King Wilhelm I of Prussia became Kaiser Wilhelm I of the German Empire. The treaties originally recognized by Prussia were now recognized by the German Empire, including the Treaty of London.
Great Britain's commitment to Belgium's neutrality was tested several times between the Franco-Prussian War and the First World War. In 1885, German Chancellor Otto von Bismarck reviewed his options in the event of another war with France. Bismark asked Britain, "Would England fight if Belgium was attacked?" The response was "No doubt, if she had an ally." Two years later, when France and Germany were on the brink of yet another war, both countries sent assurances to Belgium that her neutrality would not be violated. In 1906, British Foreign Secretary Edward Grey sought to determine what was "England's liability under the treaty [of 1839] guaranteeing the neutrality of Belgium." The conclusion was that Britain was obligated to assist if one or more of the other guaranteeing powers opposed the violation. In 1911, a series of war games showed that in a conflict between France and Germany, Germany would violate the neutrality of Belgium and possibly Holland and Denmark as well. These conclusions were made from the series of train tracks and roads that Germany had built leading to the border of Belgium. These conclusions led Winston Churchill, soon to be First Lord of the Admiralty, to send a letter to Grey that Great Britain should guarantee the independence of Belgium, Denmark, and Holland.
Great Britain's guarantee of Belgium was not just against German violation. In November of 1912, France reviewed the possibility of violating Belgium's neutrality in the event of a war with Germany. When they asked Grey for Great Britain's opinion, he said "the British Government would then be called upon to defend the neutrality of that country." After receiving such a firm stance from their ally, France renounced all ideas for such a maneuver.
In the end, it was Germany who committed the violation, even after giving assurances to Belgium in 1911 and 1913 to the contrary. On August 3, 1914, Belgium was shocked to receive Germany's 12-hour ultimatum demanding that troops be allowed to pass through without resistance. If Belgium resisted, then Germany would regard her as an enemy. Belgium responded the next day stating that they were "firmly resolved to repel every infringement of its rights by all the means in its power." At 4:00 PM that day, Belgium appealed to "England, France, and Russia to co-operate as guaranteeing Powers in the defense of her territory." Great Britain sent an ultimatum to Germany demanding that Belgium's neutrality not be violated. Germany did not respond, and at 11:00 PM August 4, 1914, Great Britain declared war. The neutrality of Belgium was more than a "scrap of paper" or an old, outdated treaty; it was a policy that had been observed and guaranteed by Britain, France, Russia, and Germany for 75 years.
Churchill, Winston S. The World Crisis, vol. 1: 1911-1914. London: The Folio Society, 2007.
Sanger, C. P. and H. T. J. Norton. England's Guarantee to Belgium and Luxemburg, with the Full Text of the Treaties. New York: Charles Scribner's Sons, 1915.
The Times. "The Eve of War." August 28, 1914.