Causes of World War 1
Alliances were some of the most difficult things. Example: Austria-Hungary went to war with Serbia, Russia got involved defending Serbia. Germany then declared war on Russia; meanwhile France was drawn against Germany and Austria-Hungary. Germany attacks France through Belgian bringing Britain into this mess of a world. Just then Japan is here, then later Italy and the U.S. come in. See, it's a really big mess.
Mr. Snyder's U.S. history text book.