1914: The Great War. German forces swiftly attack France via Belgium, according to the German Schlieffen Planm causing damage to Belgium but largely driving straight through and then sweeping into France. German forces win many key battles against Allied forces, with the UK and France continually being forced to retreat, and then retreat again.
Paris is occupied quickly by the advancing German forces, with German officials hoping that it will force France to surrender and quit the war; thereby leaving Germany to focus on the Russian front. However, the French refuse to surrender and the French war government is forced to relocate itself to Vichy, further south then Paris, in the centre of the country, and away from German lines. From Vichy, the French Army continues to put up a token resistance to the German forces. Thousands of civilians flee Paris however, in the face of the German military forces. Having dealt a massive blow to French forces, and their ability to invade Germany, German forces take their foot off the pedal.
The MP for Southampton, William Dudley Ward, dies in an accident during a Naval Reserves Exercise.
1915: The Germans attempt to fortify the front in France, without bothering to advance further west; their only objective in France is to kill any French ability to strike at the German border.
With France crippled, Germany heads east, and wins several early battles against Russia, before ploughing deeper into Russia and meeting stiffer Russian resistance in battles.
Austria-Hungary struggles against Serbia however, as a plucky defence repels many Austro-Hungarian attacks, in what has become known as the "Serbian Defence". Assisted at all costs by the British, the Serbs perform admirably, tacticly retreating where necessary, but staying in the war.
Early in 1915, the Germans attempt to force a peace with the unwilling UK, which will force peace with France by unrestrained submarine warfare against shipping in to the UK in an attempt to blockade them. However, 3 incidents of US merchant ships being torpedoed unannounced within two weeks of each other (and the subsequent deaths of many American citizens), vastly shifts opinion in the US with many now pushing for war against the Central Powers. Woodrow Wilson manages to declare war, the bill passing in Congress, although not without significant disquiet from nay-sayers, advocating that European affairs are best left to...the Europeans. With that said, by the end of the year, US soldiers are crossing the Atlantic to the UK, endeavouring to avoid German submarines.
The German High Seas Fleet also attempts a risky manoeuvre in the North Sea against the British Home Fleet in an attempt to turn up the heat against the UK and force the UK to come to terms before the US can really get involved in Europe. However, it backfires massively, when in addition to causing large damage to the Royal Navy, the High Seas Fleet is annihilated.
In Ireland, political deadlock continues, and urgently requires a resolution however. The Irish Home Rule Bill is passed, but the Province of Ulster is temporarily excluded after the Belfast Crisis; the army is unable to mobilise to fight the Ulster dissenters with the Great War ensuing (and even if it could, there is significant disquiet from many officers about the prospect of shooting at people who wish to remain loyal to Britain), and civil war looks likely if Ulster is forced in.
Ireland (all of it) remains part of the UK, but with significant devolution for (Southern) Ireland, with most international affairs remaining at the UK Government - defence, international relations, citizenship, customs & excise, amongst some others.
By the end of the year, Italy enters the war on the Allied side, after promises by Britain of a share in the war spoils. A Protectorate in Albania, and Italian speaking areas in central Europe is on offer should the Allies win the war.
1916: In the Middle East, a British invasion force invades near Syria, catching Ottoman forces unaware, and effectively almost divides the Ottoman Empire in two, helping their Arab allies in the south. The Ottoman Empire suddenly looks very, very weak.
Austria-Hungary is knocked out of the war by a combination of Serbian and Allied forces, and surrenders with Allied troops establishing occupied bases in several crucial areas of the country -although Austrian soldiers repel Italian advances until the Allies are almost behind them. The collapse of the Austro-Hungarian war effort has profound implications for Germany however, forcing some German forces to be diverted to the German - Austro-Hungarian border to prevent troops from entering Germany.
The Allied forces begin to pound the German western front, and wreak havoc upon German armies there. German forces are captured in the west by an international combination of armies (spearheaded by Empire and US forces), in a pincer attack that strands German soldiers far from lines of supply and starves them out of food and ammunition with several weeks. Germany is forced to retreat or surrender, but destroys large parts of Paris during it's surrender. Germany also annihilates much of the industry in the north-east of France and Belgium during retreat, as well as much infrastructure to slow the Allied advance. However, with the path to Germany now open (even in bad state) and Allied forces inbound - slowly, but relentlessly, Germany surrenders.
The fighting in the east is equally destructive to both the Russians and Germans, but peace is forced by the end of the year, largely by the Western Allies forcing the German withdrawal. A power vacuum forms in western Russia where German troops have eventually withdrawn, spurring revolutionary activity which rises in Russia.
In the US, following public spirit wounded by the viciousness of the war and human cost on the battle lines, President Hughes leads to the US back into "Golden Isolation" as it is termed. US Foreign Policy is chiefly focussed upon the Monroe Doctrine and little extra as it turns inwards.
Following the end of the war (which occurs at very convenient timing for the UK), the UK enacts Home Rule for (Southern) Ireland. It is promised to review the situation in Northern Ireland in 10 years as the "Ulster Exclusion" is only temporary.
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Notes: War is not my strong point, so I've avoided ultra specifics here. I'm not above fixing mistakes, so be gentle!
But the crucial point is that World War 1 is much shorter; but France and Germany are still pounded by the war effort. The shortened version of the war allows the UK to retain many resources, it retains sovereignty over Ireland (albeit with significant devolution), and ends the war as the undisputed world superpower, especially with the US withdrawing from world affairs. With Wilson entering the war before election, Hughes just wins the US Presidential election.
Britain is in a better shape, and the men of the big Dominions haven't been squandered as badly.