Britain's involvement in World War One was significant. Without the support of the U.K., France might not have been able to win the war on the Western Front. As such, the war's outcome could have been somewhat different had Britain not been involved on France's side.

In the period before 1914 Britain had increasingly come to terms with France. In 1904, the Entente Cordiale between the two countries saw a significant change in policy as Britain and France increasingly became allies. They formed a united front against Germany, whose relations with the U.K. deteriorated during the period.

By 1914, the possibility for a war in Europe had increased. Germany had drafted the Schlieffen Plan, detailing how the Germans would defeat France first before Russia in a European war. However, the plan did not reckon on Britain's involvement, assuming either that Britain would surrender if Germany defeated France or that the U.K. would not join the war.

It was not the Entente Cordiale that necessarily obliged Britain to declare war on Germany in 1914, after German troops invaded France. Britain made clear it expected that Belgium neutrality would not be violated by Germany, and that any German troop movements that violated Belgium neutrality would merit them to declare war on Germany. As such, when German troops did violate Belgium neutrality, the U.K. declared war on Germany.

Britain's involvement in the war was primarily concerned with the Western Front. As German troops swept into France, a joint effort between Anglo-French troops halted the onslaught at the Battle of the Marne. This battle saw the Schlieffen Plan fail, as the prospect of defeating France quickly evaporated. Trench warfare in the West would then see Britain commit further troops to supporting the French in Western Europe.

Britain's Royal Navy was the largest navy in the war. As such, it became one of Britain's most potent weapons against the Germans. Britain used its navy to establish an economic blockade on Germany, which became increasingly effective as the war progressed. The blockade cut military and food imports, which by 1917 resulted to food shortages in Germany. This prompted the Germans to pursue a policy of unrestricted submarine warfare in 1917, which could still not break the blockade; and the sinking of American shipping in the Atlantic prompted the USA to join the war on Britain's side. The repercussions of this were firmly felt in 1918. In addition, the Battle of Jutland was the largest naval encounter between Britain's and Germany's navies that remained an inconclusive battle, although the Royal Navy lost a higher tonnage of ships.[1]

Battle of JutlandCredit: Image licensed under public domain on Wiki Commons.  
The above image is licensed as public domain on Wiki Commons.  

Britain was also extensively involved in the Dardanelles. The Gallipoli Campaign aimed to capture the Turkish capital of Istanbul, which would secure a sea route to Russia. However, it was the biggest defeat in the war for the U.K. as it failed to secure a sea route. This campaign was the first to include the Australian and New Zealand Army Corp, and Anzac Day remains a significant commemoration of the campaign.

Despite such set backs the Entente had began to gain an advantage in the West by 1918. The prospect of increasing numbers of American troops, and Britain's naval blockade, convinced the Germans to launch a large-scale attack. After initial breakthroughs, the advance could not be sustained by Germany. An Allied counter-attack involved US, British and French soldiers. The BEF was particularly effective, making use of the tank that overran German lines. This Allied advance pushed German troops back, and such defeats prompted the abdication of Wilhelm and Germany to seek a ceasefire with the Entente.

On November 11 this ceasefire brought the war to an end. The success of the Entente counter-attack, spearheaded by British and Commonwealth troops and tanks, won the war. In Britain Remembrance Sunday, or Poppy Day, commemorates the ceasefire of November 11, 1918.