Part 1:
An Alliance is the highest of connections. An Alliance means that basically that other country is your best friend. A Treaty is simply a signed document saying that you are in agreement about an argument with another country, and that you can help them if needed. It's not one-wayed either. The treaty is for both countries. An Aid is the smallest of the three. An Aid is only a country that can give another country back up when they need it. That is all.
Part 2:
The U.S. isn't in the diagram because they didn't join the war at the start. The U.S. does join the war to give Britain back-up. In 1917, The U.S. joined WWI to join Britain and their allies, because the War started to become too serious.
An Alliance is the highest of connections. An Alliance means that basically that other country is your best friend. A Treaty is simply a signed document saying that you are in agreement about an argument with another country, and that you can help them if needed. It's not one-wayed either. The treaty is for both countries. An Aid is the smallest of the three. An Aid is only a country that can give another country back up when they need it. That is all.
Part 2:
The U.S. isn't in the diagram because they didn't join the war at the start. The U.S. does join the war to give Britain back-up. In 1917, The U.S. joined WWI to join Britain and their allies, because the War started to become too serious.