English: "The men of all Germany are preparing for war". My translation: Viri totus Germaniae bello parant. Is it correct to use bello here (dative singular since the men are preparing "for" war) or bellum (accusative singular), which is what is in the key? Why?
Accusative singular. Because although we translate paro
as "prepare" it is fully transitive in Latin. In Latin one does not so much prepare for
a war as prepare
a war, as one might prepare a meal or plan
a war. The war is not the indirect, but the direct object of the preparations.
The equal but opposite trap is with verbs like pareo
(I obey), which are transitive in English but intransitive in Latin, and therefore take an indirect object which is in the dative.