[2ndDivisionVet]

Zimmermann Telegram
http://en.wikipedia.org/wiki/Zimmermann_Telegram

[dsm69]

Yes, the Zimmermann Note, along with the Germans re-instating unrestricted U-boat warfare just prior to the Zimmermann Note being made public, caused U.S. entry into WWI.

[bvw]

Ditto.

[bvw]

To clarify my ditto to 2DV.

I mean the works of military historian Barbara Tuchman on the WWI era are the best starting resource. Her's is the most comprehensive coverage, although I will give the final summary in the last paragraph here.

Barbara Tuchman's books on this issue, in the order I suggest they be read:

1. The Guns of August
2. The Zimmermann Telegram
3. The Proud Tower

There are almost NO historians in all of history at the rank of Mrs. Tuchman. Her works are rare gems.

Now to the summary: The USA could not have avoided getting involved in WWI! That's as hard a fact as that of water being wet.