World War I still evokes controversy, after almost 104 years. As the prima facie event of the 20th Century – as it led to all the others – one must ask: what if things had been different?? What if the Germans, instead of following their rigid Schlieffen Plan, invaded through just Luxembourg and France?? What implications would this have on the outcome of the Battle of the Marne, indeed the war itself?? Would Britain have gotten involved??
All these questions remain unanswered precisely because the Germans, in the end, and to the surprise and shock of all of Europe, did invade Belgium.  But let’s suppose for a moment that Germany did not invade Belgium. Would Britain have entered the war??
The most plausible answer to this is a qualified maybe. In the summer of 1914, Britain was in perhaps its worst political and constitutional crisis ever. The issue of the day: not the simmering tensions of Europe, but those of Northern Ireland. In 1912, the Liberal Government passed Irish Home Rule, a bill that was due to become law in the Autumn of 1914. The law was to give all of Ireland autonomy, but also provided for a single Irish Dominion. Protestants in the North violently objected to this, as they feared that they would be overwhelmed by the Catholic South. In the Spring of 1912, several soldiers mutinied and refused to carry out orders to quall the Protestant rebellions. During the Summer of 1914, Britain looked as it was in a state of civil war. 
And then – suddenly – World War I breaks out, a war which can only unify the nation. A classic interpretation of the origins of World War I put this as a chief cause. 
Upon closer look, however, one finds the picture to be much more cloudy than that. The Liberal Government was deeply divided over going to war with Germany. Within the Liberal Party, there was a strong Glastonian pacifist tradition. Many would not contenance a war against Germany solely to protect France, despite the 1904 Entente Cordiale [which was only an agreement to settle colonial disputes in Africa]. There was no clear majority for going to war , rather there was a tilt toward staying out of it.  For sure, there were influential members of the Cabinet, such as Sir Edward Grey [the Foreign Secretary] and Winston Churchill [then the First Lord of the Admiralty], who were in favor of war regardless of the Belgian issue, but they were in a clear minority. If not most of the Cabinet, most of the Liberal Party did not want war.
If Britain had gone to war without the Belgian casus belli, it is likely that half, and perhaps more, of the Cabinet would have resigned in protest. Asquith would have had to form a Coalition Government with the Conservatives. While it would have been able to carry on the war, it is likely that this war effort would have been hampered seriously by a “peace party.” Recruitment would have been hampered, and Britain’s war effort would have been seriously affected.
Finally, another point to ponder. If Britain stayed neutral, Barbara Tuchman argues in her famous book, The Guns of August, the Schlieffen Plan would most probably have had worked.  Paris would have fallen, the Germans would have won the war, and this would be a different world today. Perhaps it would have been better … as in no Hitler, no Holocuast, no Soviet Union, etc. One should not pursue this too far, as you cannot change history, but it is certainly a fun and useful exercise!!
-  Barbara W. Tuchman, The Guns of August, (NY: The Macmillan Company, 1962), p. 123.
- Many, including the French, thought that the German ultimatum to Belgium on August 1, was a trick designed to get France to invade Belgium first. As a precautionary measure, the French ordered their armed forces to fall back 10 km., an unprecedented action during wartime. (See Tuchman, p. 84.)
-  Peter Clarke, Hope and Glory: Britain, 1900-1990, (NY: Penguin Books, 1996), p. 69.
-  George Dangerfield, The Strange Death of Liberal England, 1910-1914, (NY: Capricorn Books, 1961), 2nd ed., p. 422.
-  Martin Gilbert, The First World War, (NY: Henry Holt and Company, 1994), p. 32.
-  A.J.P. Taylor, ed. by Chris WrigleyFrom the Boer War to the Cold War: Essays on Twentieth Century Europe, (NY: Penguin, 1994), p. 171.
-  Tuchman, pp. 436-37.