On 8 April 1918, after the defeat in Tampere and the German army intervention, the People's Delegation retreated from Helsinki to Vyborg. The loss of Helsinki pushed them to Petrograd on 25 April. The escape of the leadership embittered many Reds, and thousands of them tried to flee to Russia, but most of the refugees were encircled by White and German troops. In the Lahti area they surrendered on 1-2 May. The long Red caravans included women and children, who experienced a desperate, chaotic escape with severe losses due to White attacks. The scene was described as a "road of tears" for the Reds, but for the Whites, the sight of long, enemy caravans heading east was a victorious moment. The Red Guards' last strongholds between the Kouvola and Kotka area fell by 5 May, after the Battle of Ahvenkoski. The war of 1918 ended on 15 May 1918, when the Whites took over Fort Ino, a Russian coastal artillery base on the Karelian Isthmus, from the Russian troops. White Finland and General Mannerheim celebrated the victory with a large military parade in Helsinki on 16 May 1918. The Red Guards had been defeated. The initially pacifist Finnish labour movement had lost the Civil War, several military leaders committed suicide and a majority of the Reds were sent to prison camps. The Vaasa Senate returned to Helsinki on 4 May 1918, but the capital was under the control of the German army. White Finland had become a protectorate of the German Empire and General Rüdiger von der Goltz was called "the true Regent of Finland". No armistice or peace negotiations were carried out between the Whites and Reds and an official peace treaty to end the Finnish Civil War was never signed.
Question: What caused the end of the war on 15 May 1918?
Answer: Whites took over Fort Ino