Kammala wannan jumla: Bayan shigar Amurka cikin yaƙin Turai a bazara na 1917, Magnes ya mai da hankalinsa ga kamfen ɗin adawa da shi. Ya zama daya daga cikin manyan shugabannin kungiyar. Kamar yawancin shugabanninta ya nuna juyayi ga masu aiki. Mutane irin su Eugene Debs wanda aka yanke masa hukuncin shekaru goma a kurkuku saboda ayyukansa; Norman Thomas; Roger Nash Baldwin; Scott Nearing; Morris Hillquit, wanda ya dauki kashi 22% na kuri'un a zaben New York na Mayor a kan wani dandalin yaki; da Oswald Garrison Villard. Yawancin waɗannan mutanen sun shiga cikin abin da ya zama Majalisar Jama'ar Amurka don Demokradiyya da Zaman Lafiya tare da Magnes shugabanta na farko. A ranar 30 ga Mayu 1917 ya ba da jawabi ga taron taro na mutane dubu goma sha biyar a cikin
Gidan shakatawa na Madison Square. An dakatar da wani taron ci gaba a Minneapolis kuma an sake sake shi a Chicago amma tare da sojojin soja suna barazanar karya shi. Magnes ya koma gida a Connecticut saboda adawa daga maƙwabtansa kuma wani wakili daga Ma'aikatar Shari'a ya yi hira da shi. Daya daga cikin abokan aikinsa daga "Joint", B. D. Bogen, Babban Lauyan ya yi masa tambayoyi game da ayyukan Magnes. Magnes ya yi aiki tare da sabon ofishin 'Yancin Bil'adama wanda ya kare masu zaman lafiya da masu bin lamiri. A cikin Amurka an gabatar da tuhume-tuhume sama da 2,000 a kan masu adawa da yaƙi a ƙarƙashin Dokar Haɓaka ko Dokar leken asiri; Magnes ya guji gurfanar da shi saboda ya wuce shekarun da za a ɗauke shi aiki.