I wanted to find the answers to these WWI questions and here is what I found...

1. WWI started on July 28, 1914 because Austria's Archduke, Franz Ferdinand was assassinated. The combatants of the war were the Allies who were France, British Empire, Russia, Italy, U.S., Serbia, Montenegro, Romania, Japan, Brazil, Portugal, Greece and Belgium, and the Central forces who were Germany, Austria-Hungary, Ottoman Empire, and Bulgaria.
2. The U.S. got involved in the war on April 6, 1917 because Germany sunk 7 U.S. merchant ships by submarines.
3.

Casualties of WWI

4. WWI ended on November 11, 1918 when Germany signed an armistice with the Allies.