Leaders and Co-leaders can take their Clan to War by opening the Clan War screen and pressing the “Start War” button. Please note, you must have 10 members or over to begin. 

This will start the search for an opposing clan. The matchmaking system will ensure your Clan is paired up with a Clan of equal Strength (both attack and defense) and a similar number of Clan members. The Clan War will start immediately after a suitable opponent has been found. 

Finding an opposing Clan can take several minutes, but there is no need to wait in the matchmaking screen. Just press the 'Return Home' button to continue playing, and you will be notified when an opponent has been found.