declare war
/dɪˈkleər wɔːr/
Meaning
Officially, this means to make a formal announcement that a state of war exists between countries. Metaphorically, in daily life, it means to start a vigorous, determined campaign against something undesirable (like clutter, insects, or bad habits) or to start a major conflict with someone.
Examples
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My mother declared war on the dust in the living room and spent all Sunday cleaning.
My mother declared war on the dust in the living room and spent all Sunday cleaning.
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In 1917, the United States officially declared war on Germany.
In 1917, the United States officially declared war on Germany.
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The government has declared war on plastic waste with its new recycling policy.
The government has declared war on plastic waste with its new recycling policy.
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My neighbor declared war on me after I accidentally cut down his favorite rose bush.
My neighbor declared war on me after I accidentally cut down his favorite rose bush.
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I've declared war on sugar, so I'm cutting out all soda and candy from today.
I've declared war on sugar, so I'm cutting out all soda and candy from today.
Common Mistakes
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✗ The country declared a war against its neighbor.
✓ The country declared war on its neighbor.
The standard collocation is 'declare war' (usually without the article 'a') and it takes the preposition 'on', not 'against'.
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✗ She made a declaration of war to her messy bedroom.
✓ She declared war on her messy bedroom.
While 'declaration of war' is grammatically correct, using the verb form 'declared war on' is far more natural for daily, metaphorical contexts.
Related Expressions
Practice
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The city has decided to ___ on littering by doubling all fines.
💡 Start a major, determined campaign against something undesirable.
Show answer
declare war
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Historically, only congress has the power to ___.
💡 Officially announce a state of military conflict.
Show answer
declare war