U.S. History

Here's a good PBS resource, with some animations that set the scene.

Here's a better map.

Here are the alliances in more detail.

This is a good explanation/diagram of the Schlieffen Plan.

The moral: Try not to fight a two-front war

Here are more resources from Wikipedia.

Casualties from World War I

The influenza virus of 1918 in the United States (see the map)

Worldwide, the flu probably killed 20-40 million people.