In what instances can the word 'war' on its own i.e. without numerals and/or names/titles be used without any article?

Question

Negotiations broke down and war was declared.

War broke out between the two countries.

Answer 1

"War" has several noun definitions, including:

• a conflict
• a state of conflict.

Both your examples refer to declarations of war which are a state or situation, which is why they do not require an article.

Consider as an example:

• Swimming takes place at the pool.

"Swimming" is here used as a noun for the act of swimming. There is no need for an article.

• You can have a swim at the pool.

"Swim" is also a noun here, but because it refers to a specific swim, an article is used.

Likewise:

• There is war in the middle east (refers to a current state)
• There is a war in the middle east (refers to a specific conflict).