war cry 
noun
A call made to rally soldiers for battle or to gather together participants in a campaign.A former regimental sergeant major has issued a war cry to pensioners to back our campaign to save three under-fire post offices....
- A ball of fire erupted out, shattering the susurration with a jarring war cry.
- The two bellowed a war cry and charged at each other.
Synonyms
battle cry, war whoop, rallying call