Full Idea
Each state must be organised so that the head of state, for whom the war costs nothing (for he wages it at the expense of the people) must no longer have the deciding vote on whether war is to be declared or not, for the people who pay for it must decide.
Gist of Idea
The people (who have to fight) and not the head of state should declare a war
Source
Immanuel Kant (True in Theory, but not in Practice [1792], 3)
Book Reference
Kant,Immanuel: 'Political Writings', ed/tr. Reiss,Hans [CUP 1996], p.90
A Reaction
I would guess that he has Louis XIV particularly in mind. Imagine if Kant's proposal had been implemented in 1914. A referendum takes ages, and the people would need the facts (from the intelligence agencies).