4. What did Germany offer Mexico if Mexico would side with Germany in the war?

The Zimmerman Telegram.

Explanation:

The Germans would provide military and financial support for a Mexican attack on the United States, and in exchange Mexico would be free to annex "lost territory in Texas, New Mexico and Arizona." Coupled with the submarine attacks, it finally turned the U. S. government in favor of entering the fray.

the germans offered new mexico arizona, and texas to mexico if they sided with the central powers via the zimmermann telegram.