Yes. If your town is under Peace Treaty and you try to send your troops to the resource location which has been already captured by another player you will see this message;  If you send your troops to attack or spy, the Peace Treaty will lose its power. Are you sure you want to proceed?" If you click "Yes" button the Peace Treaty will expire immediately. However, if you send your troops to uncaptured resource location but someone else's army reaches the same location before your army, your troops will return to their home, you will receive The town has Peace Treaty notification message and you won't lose your Peace Treaty.