Which of the following was not discussed in the Zimmerman Telegram?

The Zimmerman Telegram, sent from Germany to Mexico in January 1917, primarily focused on the proposal of a military alliance between Germany and Mexico in the event that the United States entered World War I. The telegram promised Mexico the territory it had lost to the United States in the mid-19th century, specifically Texas, New Mexico, and Arizona, thus directly addressing parts A and C, which are closely tied to its content.

As for unrestricted submarine warfare, it was indeed a significant aspect of Germany's military strategy during World War I, aimed at disrupting Allied supply lines. This relates to option D which discusses the execution of such warfare.

However, option B refers to "militarist plans for Eastern Europe," which was outside the scope of the Zimmerman Telegram's discussions. The telegram's focus was distinctly on the relationship between Germany and Mexico and did not elaborate on Europe’s broader military situation or strategize about Eastern Europe specifically. Therefore, this context solidifies why this particular option is not aligned with the contents of the Zimmerman Telegram.