What is the status of Christians in Islam, and are they considered disbelievers or enemies, especially given the permissibility of marrying them and eating their food?

Allah has permitted marriage to the women of the People of the Book and eating from their slaughtered animals, as an exception for them. Every disbeliever is an enemy to Allah, His Messenger, and the believers because of their disbelief, so there is no alliance between them and the Muslims. As for peace and war, they are not all the same; among them are the belligerent and the peaceful, and the Shari'ah has detailed how to deal with each type.