100 years ago today, the landings on Gallipoli Peninsular took place. The campaign was the brainchild of Winston Churchill basically - the idea was for the allies to force their way up the Dardenelles and take Constantinople, giving them access to the Black Sea, and thus Russia. There's a lot of backstory to this battle. Start with the Ottoman Empire deciding to join the Germans and Austrians in the war. The Young Turks hwo rules the Ottoman empire were close to the Germans - the British tended to be more bullying, while the Germans offered help and support - the Turks chose Germany. That shut off the Dardenelles, and most significantly, cut off sea routes to Russia. The Russians in 1914 were desperately short of supplies - England and France had no way to get them material. So Churchill and company thought to force their way up the Dardenelles, take Constantinople, and open the shipping lanes to the Black Sea.
Churchill tried first to do it with naval power alone. Battleships were sent, they bombarded the Turkish defenses, then tried to steam up the straights - only to be devastated by mines, primarily. Several ships sank - the fleet retreated. After this, the army was sent in. The idea was to find and destroy the Ottoman artillery - the guns hadn't done much against the battleships, but they had driven off the minesweepers, leaving the battleships helpless against mines. And so - on April 25, 1915, troops were put ashore at several beaches on the Gallipoli peninsular.
The landings were a disaster. Amphibious landings under fire were still something of a novelty - getting men ashore was not easy. What's worse - the Allies did not really know what they were getting into. The ANZAC forces landed a mile off from where they were supposed to land - across the whole area, the Allies did not understand the lay of the land, the conditions on the beaches and so on. They didn't have any idea of the strength of the men waiting for them. They landed in the face of determined resistance, from men dug in on high ground, from positions that allowed crossing fire - they never had a chance. Casualties ran 60-70% in most of the battlegrounds - by the end of the first day, the British and ANZAC forces had managed to take a strip of land by the beaches, but no more. And they never went anywhere in the next 7 months. Because as bad as the landings went, once the Turks were able to bring in enough men to hold the ground, they had the allies completely at their mercy. They had the high ground - they had positions that let them rake the allied positions - the battle quickly turned into protracted trench warfare. It was probably worse than anything on the western front, too - the peninsular was dry and hot, and what fresh water there was was controlled by the Ottomans - water had to be brought in to the allied forces - every thing had to be brought ashore to the allies forces. And there was never enough - the trenches became hellish and stayed that way.
In the end, the allies left, losing 250,000 odd men. The Turks lost about the same, but they won, expelling the invaders. As far as the war went, it was just another of the many pointless and hopeless battles that accomplished nothing but very long casualty lists. Beyond the war, though, it has a great deal of importance. It was a great moment in Turkish nationalism - the victory had great importance to their morale, and provided a source of national pride. It also elevated Mustafa Kemal (later Attaturk) to prominence. It had a similar effect in Australia and New Zealand. The heroism and suffering of the ANZAC troops made Gallipoli the definitive campaign for those countries. And their use - the sense of being thrown into battle half prepared, and of beings used as distractions and covers for the British (an idea that is not really fair) - led to resentment in Australia and New Zealand against the British, and helped to form the idea of those countries as nations unto themselves. It strengthened their sense of independence - the emergence of their sense of national character. It has made today, April 25, a national holiday in both countries, and made it the most important military commemoration as well.