(A lot of this 'History' is pure bullshit, but I need it to add Tyrrhenia to the 'World'.)
The island nation of Tyrrhenia has long been seen as a haven of pirates, ne'er do wells and the scum of the earth. Pirate nests in the bays and coves preyed on the merchant ships that plied their trade throughout the Mediterranean and were forced by geography to pass by the traps of Tyrrhenia. Many nations took some or all of Tyrrhenia during its long and nefarious career. It was part of the Greek, Roman, Carthaginian, Ottoman, and Spanish Empires at various stages from BC times through to the 14th century. From the 15th century on the Knights Templar ruled Tyrrhenia defeating the French Empires efforts to destroy the Templar hold. The guarantee for the Templar rule came from the English who at that stage were at odds with the Roman Catholic Empire and by extension also France and Spain. Though backed by Britain, Tyrrhenia was never part of the British Empire. During the First World War the Tyrrhenians fought on the Allied side. But during the period between the wars, the Tyrrhenians were seduced by the words of Il Duce and with disputes with Britain over access to the Island of Malta (between Crete and Cyprus) which had been leased to the British during the Peninsular and Bonaparte wars. The 99 year lease had already been extended once and had expired again in 1932. The British had put extreme pressure on the Tyrrhenian Government to renew the lease as Malta formed a pivotal point for the British Mediterranean Fleets wellbeing. Il Duces whisperings fell on fertile ground. The Tyrrhenian Government remained neutral during the 1939-40 period of World War Two but threw in with the Axis along with Italy on the surrender of France in July 1940.
The forming of the Vichy French Government covered the backs of the Italian and Tyrrhenian forces in the North African Theatre during 1940-41. The Army and Air Force battles raged backwards and forwards as the British pushed one way then had to retreat as the Axis forces were strengthened with Rommel's Africa Corps. The Combined navies of Italy and Tyrrhenia were bigger than the Mediterranean Fleet of the British. But crucially the Axis Fleets had no aircraft carriers. This proved to be the difference with the Commonwealth forces attacking and sinking a large proportion of the Italian Fleet at its moorings in Taranto Harbour.
Though there was only half a mile of water between Malta and Cyprus, the current through that gap at nearly 5 knots. This does not sound much but together with the cliffs of Malta and the defenses of the British, the two attacks mounted by the Tyrrhenian forces to take Malta failed miserably. It was left to the German Parachute Division to take Malta during 1941 and leave the reinforcements to North Africa unmolested by air and sea with only the Commonwealth submarines taking any toll.
With the Americans joining the war in December 1941, the US and Commonwealth forces take out Vichy North Africa and squeeze the Axis forces between the east and west Allied forces with many thousands of troops having to be abandoned as Allied Air, Land and Sea power totally overwhelmed the Axis forces and they cut their losses and with drew their troops back to Tyrrhenia and Italy. German troops going to each country to stiffen their resistance.
1943 and the Allies control all of North Africa. They can strike at the Axis wherever they choose. However, the more moderate factions in the Tyrrhenian Government want the 'Nazi' section of their Government out, and to go back to being an ally of the Commonwealth as they had been for over 300 years. An envoy is sent to the Allied High Command with the offer that if the Allies attack the Tyrrhenian Archipelago the Tyrrhenian forces will lay down their arms and surrender, leaving just the German Forces for the Allies to subdue with force of arms. To show their intent is real, the Tyrrhenian envoy produced an order of battle of all the German forces on Tyrrhenian lands and a map showing exactly where they were. Needless to say, the chance of an easy victory over the German forces and the removal of an Axis power from the fight proved irresistible. August 1943 and Tyrrhenia surrenders to the invading Allied forces.
While the Tyrrhenian forces had surrendered, the Allies, with the US Government in the lead, held the Tyrrhenian forces in their homeland as the reparation package that Tyrrhenia would have to pay was worked out. It was fortunate for Tyrrhenia that they had refused to send forces to help out the Axis forces in Russia. Had they done so, the Russians would have wanted their pound of flesh as well. What made a difference was that a lot of Tyrrhenians had emigrated to the United States, starting from the late 1880's as mechanisation took the jobs away and the only place to go was the 'new world'. Many of those people were now in positions of power and could help to influence the deliberations of the Allies.
The Teheran Conference of November-December 1943, set the terms of Tyrrhenias return to the Allied fold. It was at this conference that Stalin was told that Russia would have no part of any Tyrrhenian reparations. Stalin not happy.
October 1943, the major Tyrrhenian ports are used as the springboard for the Allied invasion of Italy. Since Tyrrhenia had surrendered the Italians had also become unhappy with continuing the war on the side of the Axis. The Italian Government of Il Duce was being held up with German support and the German troops that were put beside the Italian troops to stiffen their resolve.
Once the Italian invasion was underway, Tyrrhenia became a backwater with just a few garrison troops to ensure Tyrrhenia remained 'surrendered'.
There was an area termed "Tyrrhenia" in times past, like 200-65 million years ago, but it was a land mass that occupied an area in what is now the Western Mediterranean basin, the only bits of which are left is Corsica and Sardinia. This land mass has no resemblance to my Alternate Tyrrhenia which I have placed where I have so that it can have more of an impact on Mediterranean Politics and WW2.