Answer:Zimmerman Telegram and Germany's admitting to enter into unrestricted submarine warfare
Explanation:
Zimmerman Arthur,is a German diplomat and its foreign secretary who admitted that the Zimmerman Telegram was true and that its contents are true. German in that telegram was planning to form an alliance with Mexico to recover New Mexico, Texas and Arizona from United States of America should the United States of America go into world war 1 in 1917,so his admittance caused disaffection Among United States citizens.
Germany started an unrestricted submarine warfare with United States of America on First of February,1917 because they believe United States of America will be to slow to defeat them.