Woodrow Wilson was president of the United States. Herbert Henry Asquith was prime minister of England till 1916 and then David Lloyd George took over. Raymond Nicolas Landry Poincaré was president of France. Jean Raphaël Adrien René Viviani was the prime minster of France. Sir Robert Laird Borden was prime minister of Canada. Emperor Taishō, Peter I of Serbia, Venceslau Brás (president of Brazil), Constantine I (king of Greece), Rama V (king of Siam which is now called Thailand), Albert I (King of Belgium), Victor Emmanuel III (King of Italy), Afonso Augusto da Costa (prime minister of Portugal), Ferdinand I King of Romania) were also allies. Tsar Nicholas II was the head of Russia and Poland. Russia dropped out of the war before it ended.
On the Central Powers side there was Kaiser Wilhelm of Germany, Emperor Franz Joseph I of Austria, and Enver Pasha who was the minister of war for Turkey under Sultans Mehmed V and VI.