Mack - This is a sticky wicket indeed.
The American press made it appear that the sinking of the Lusitania was justification to enter the was agasinst the Central Powers. There is no legal basis for this.
The final blow came when it was claimed that the SS Sussex had also been sunk, with American casualties. This was a deliberate lie spread by the Admiralty and the US Press. The Sussex was safe.
http://letters.frontpagemag.com/cgi-...pl?article=750
At this point, we get into international intrigue, The Balfour Declaration, statements by a whistleblower named Ben Freedman, etc..
I don't know if this forum wants to go into this matter. It is quite sensitive. You can investigate it all with Google.
In any even, the USA could have easily handled any problem with Mexico.