Learning by Teaching: Ban on Preemptive War

Came across this while teaching World War II in my AP US History class. The Ludlow Amendment, first proposed in 1935, would have required a national vote on any declaration of war by Congress, unless the US had attacked. Here's the exact wording:

SEC. 1. Except in the event of an invasion of the United States or its Territorial possessions and attack upon its citizens residing therein, the authority of Congress to declare war shall not become effective until confirmed by a majority of all votes cast thereon in a Nation-wide referendum. Congress, when it deems a national crisis to exist, may by concurrent resolution refer the question of war or peace to the citizens of the States, the question to be voted on being, Shall the United States declare war on ________? Congress may otherwise by law provide for the enforcement of this section.

I like the idea and the clarity of the wording. Despite harsh criticism from President Roosevelt, the bill almost passed with a vote of 209 to 188.