How we cite our quotes: (Sentences numbered)
Quote #1
We intend to begin on the 1st of February unrestricted submarine warfare. (1)
Killing women and children who happen to be crossing the Atlantic during a war isn't the point here. The important thing is how Germany has found a practical solution to the pesky issue of the British navy controlling entire oceans and continuing to trade with so-called neutral nations.
Quote #2
[…] we make Mexico a proposal of alliance on the following basis: make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico and Arizona. (3)
Germany isn't friends with Mexico. They aren't even chums who go like to have drinks after work. Germany needs something from Mexico and maybe Mexico can get something out of the arrangement too. This is an uncomplicated arranged marriage—or it might have been if people hadn't found out about it.
Quote #3
The settlement in detail is left to you. (4)
Germany doesn't really care what happens as long as they get what they want out of this relationship. Mexico could overthrow all of North America and turn the entire continent into a massive amusement park. Or they could fail miserably and lose another third of their land to the Americans. It's all cool as long it doesn't interrupt unrestricted submarine warfare because that's all that really matters.