Woodrow Wilson was the President of the United States during this time period. He first advocated neutrality when this war started in 1914. By 1917, after Germany had invaded Belgium, violated international law, and sank a British boat that had Americans on board, he changed his policy of neutrality and declared war against Germany on April 6, 1917.
Allies
Nicholas II was the czar of Russia during World War I. Under his command, the Russian army fought unsuccessfully on the Eastern Front. Because of this his popularity fell greatly and many thought a revolution would happen. He finally gave up his thrown on March 15, 1917 under the recommendation of the Russian Army High Command. In 1917, the Bolsheviks took over the Russian government and Nicholas II and his family were assassinated in 1918.
Marshal Ferdinand Foch had many successes in battle and so was first appointed to be in charge of the French Northern army. In 1918 he was promoted to the position of Allied Supreme Commander. He received much credit for the victory over Germany, and he also was involved in the Paris Peace Conference and the Creation of the Armistice.
Vittorio Orlando became Italy's Prime Minister in 1917. He replaced the Chief of Staff, and the next year Italy saw success during the battle of Vittorio Veneto. He remained Prime Minister till the end of the war and was involved at the Paris Peace Conference .
Enemies
Kaiser Wilhelm II was the emperor of Germany during World War I. After the assassination of the Archduke he encouraged Austria-Hungary to take revenge against Serbia. Germany almost won the war in 1918 , but later their success collapsed after United States involvement. After this, Wilhelm gave up the thrown and lived in exile in the Netherlands for 20 years.
Franz Josef was the Emperor of Austria-Hungary. He issued an ultimatum to Serbia and then declared war on them after Serbia didn't meet one of their demands. By 1916 he thought that victory for his side of the war was impossible.